scripts: Add makefile.clang, makefile.clang-asan and makefile.gcc-asan

Also apply minor updates to makefile.gcc and makefile.msys
diff --git a/scripts/makefile.clang b/scripts/makefile.clang
new file mode 100644
index 0000000..fcaefae
--- /dev/null
+++ b/scripts/makefile.clang
@@ -0,0 +1,87 @@
+# makefile for libpng using clang (generic, static library)
+# Copyright (C) 2008, 2014 Glenn Randers-Pehrson
+# Copyright (C) 2000, 2014, 2019 Cosmin Truta
+# Copyright (C) 1995 Guy Eric Schalnat, Group 42, Inc.
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# Location of the zlib library and include files
+ZLIBINC = ../zlib
+ZLIBLIB = ../zlib
+
+# Compiler, linker, lib and other tools
+CC = clang
+LD = $(CC)
+AR_RC = ar rcs
+RANLIB = ranlib
+CP = cp
+RM_F = rm -f
+
+WARNMORE = -Wwrite-strings -Wpointer-arith -Wshadow \
+	-Wmissing-declarations -Wtraditional -Wcast-align \
+	-Wstrict-prototypes -Wmissing-prototypes # -Wconversion
+CPPFLAGS = -I$(ZLIBINC) # -DPNG_DEBUG=5
+CFLAGS = -W -Wall -O2 # $(WARNMORE) -g
+LDFLAGS = -L$(ZLIBLIB)
+LIBS = -lz -lm
+
+# File extensions
+EXEEXT =
+
+# Pre-built configuration
+# See scripts/pnglibconf.mak for more options
+PNGLIBCONF_H_PREBUILT = scripts/pnglibconf.h.prebuilt
+
+# Variables
+OBJS =  png.o pngerror.o pngget.o pngmem.o pngpread.o \
+	pngread.o pngrio.o pngrtran.o pngrutil.o pngset.o \
+	pngtrans.o pngwio.o pngwrite.o pngwtran.o pngwutil.o
+
+# Targets
+all: static
+
+pnglibconf.h: $(PNGLIBCONF_H_PREBUILT)
+	$(CP) $(PNGLIBCONF_H_PREBUILT) $@
+
+.c.o:
+	$(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $<
+
+static: libpng.a pngtest$(EXEEXT)
+
+shared:
+	@echo This is a generic makefile that cannot create shared libraries.
+	@echo Please use a configuration that is specific to your platform.
+	@false
+
+libpng.a: $(OBJS)
+	$(AR_RC) $@ $(OBJS)
+	$(RANLIB) $@
+
+test: pngtest$(EXEEXT)
+	./pngtest$(EXEEXT)
+
+pngtest$(EXEEXT): pngtest.o libpng.a
+	$(LD) $(LDFLAGS) -o $@ pngtest.o libpng.a $(LIBS)
+
+clean:
+	$(RM_F) *.o libpng.a pngtest$(EXEEXT) pngout.png pnglibconf.h
+
+png.o:      png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngerror.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngget.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngmem.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngpread.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngread.o:  png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrio.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrtran.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrutil.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngset.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngtrans.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwio.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwrite.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwtran.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwutil.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+
+pngtest.o:  png.h pngconf.h pnglibconf.h
diff --git a/scripts/makefile.clang-asan b/scripts/makefile.clang-asan
new file mode 100644
index 0000000..0cab52f
--- /dev/null
+++ b/scripts/makefile.clang-asan
@@ -0,0 +1,87 @@
+# makefile for libpng using clang + address sanitizer (generic, static library)
+# Copyright (C) 2008, 2014 Glenn Randers-Pehrson
+# Copyright (C) 2000, 2014, 2019 Cosmin Truta
+# Copyright (C) 1995 Guy Eric Schalnat, Group 42, Inc.
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# Location of the zlib library and include files
+ZLIBINC = ../zlib
+ZLIBLIB = ../zlib
+
+# Compiler, linker, lib and other tools
+CC = clang
+LD = $(CC)
+AR_RC = ar rcs
+RANLIB = ranlib
+CP = cp
+RM_F = rm -f
+
+WARNMORE = -Wwrite-strings -Wpointer-arith -Wshadow \
+	-Wmissing-declarations -Wtraditional -Wcast-align \
+	-Wstrict-prototypes -Wmissing-prototypes # -Wconversion
+CPPFLAGS = -I$(ZLIBINC) # -DPNG_DEBUG=5
+CFLAGS = -W -Wall -O0 -g -fsanitize=address
+LDFLAGS = -L$(ZLIBLIB) -g -fsanitize=address
+LIBS = -lz -lm
+
+# File extensions
+EXEEXT =
+
+# Pre-built configuration
+# See scripts/pnglibconf.mak for more options
+PNGLIBCONF_H_PREBUILT = scripts/pnglibconf.h.prebuilt
+
+# Variables
+OBJS =  png.o pngerror.o pngget.o pngmem.o pngpread.o \
+	pngread.o pngrio.o pngrtran.o pngrutil.o pngset.o \
+	pngtrans.o pngwio.o pngwrite.o pngwtran.o pngwutil.o
+
+# Targets
+all: static
+
+pnglibconf.h: $(PNGLIBCONF_H_PREBUILT)
+	$(CP) $(PNGLIBCONF_H_PREBUILT) $@
+
+.c.o:
+	$(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $<
+
+static: libpng.a pngtest$(EXEEXT)
+
+shared:
+	@echo This is a generic makefile that cannot create shared libraries.
+	@echo Please use a configuration that is specific to your platform.
+	@false
+
+libpng.a: $(OBJS)
+	$(AR_RC) $@ $(OBJS)
+	$(RANLIB) $@
+
+test: pngtest$(EXEEXT)
+	./pngtest$(EXEEXT)
+
+pngtest$(EXEEXT): pngtest.o libpng.a
+	$(LD) $(LDFLAGS) -o $@ pngtest.o libpng.a $(LIBS)
+
+clean:
+	$(RM_F) *.o libpng.a pngtest$(EXEEXT) pngout.png pnglibconf.h
+
+png.o:      png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngerror.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngget.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngmem.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngpread.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngread.o:  png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrio.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrtran.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrutil.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngset.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngtrans.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwio.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwrite.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwtran.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwutil.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+
+pngtest.o:  png.h pngconf.h pnglibconf.h
diff --git a/scripts/makefile.gcc b/scripts/makefile.gcc
index ba92d15..a977313 100644
--- a/scripts/makefile.gcc
+++ b/scripts/makefile.gcc
@@ -1,6 +1,6 @@
 # makefile for libpng using gcc (generic, static library)
 # Copyright (C) 2008, 2014 Glenn Randers-Pehrson
-# Copyright (C) 2000 Cosmin Truta
+# Copyright (C) 2000, 2014, 2019 Cosmin Truta
 # Copyright (C) 1995 Guy Eric Schalnat, Group 42, Inc.
 #
 # This code is released under the libpng license.
@@ -24,7 +24,7 @@
 	-Wstrict-prototypes -Wmissing-prototypes # -Wconversion
 CPPFLAGS = -I$(ZLIBINC) # -DPNG_DEBUG=5
 CFLAGS = -W -Wall -O2 # $(WARNMORE) -g
-LDFLAGS =
+LDFLAGS = -L$(ZLIBLIB)
 LIBS = -lz -lm
 
 # File extensions
@@ -63,7 +63,7 @@
 	./pngtest$(EXEEXT)
 
 pngtest$(EXEEXT): pngtest.o libpng.a
-	$(LD) $(LDFLAGS) -L$(ZLIBLIB) -o $@ pngtest.o libpng.a $(LIBS)
+	$(LD) $(LDFLAGS) -o $@ pngtest.o libpng.a $(LIBS)
 
 clean:
 	$(RM_F) *.o libpng.a pngtest$(EXEEXT) pngout.png pnglibconf.h
diff --git a/scripts/makefile.gcc-asan b/scripts/makefile.gcc-asan
new file mode 100644
index 0000000..aae55d6
--- /dev/null
+++ b/scripts/makefile.gcc-asan
@@ -0,0 +1,87 @@
+# makefile for libpng using gcc + address sanitizer (generic, static library)
+# Copyright (C) 2008, 2014 Glenn Randers-Pehrson
+# Copyright (C) 2000, 2014, 2019 Cosmin Truta
+# Copyright (C) 1995 Guy Eric Schalnat, Group 42, Inc.
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# Location of the zlib library and include files
+ZLIBINC = ../zlib
+ZLIBLIB = ../zlib
+
+# Compiler, linker, lib and other tools
+CC = gcc
+LD = $(CC)
+AR_RC = ar rcs
+RANLIB = ranlib
+CP = cp
+RM_F = rm -f
+
+WARNMORE = -Wwrite-strings -Wpointer-arith -Wshadow \
+	-Wmissing-declarations -Wtraditional -Wcast-align \
+	-Wstrict-prototypes -Wmissing-prototypes # -Wconversion
+CPPFLAGS = -I$(ZLIBINC) # -DPNG_DEBUG=5
+CFLAGS = -W -Wall -O0 -g -fsanitize=address
+LDFLAGS = -L$(ZLIBLIB) -g -fsanitize=address
+LIBS = -lz -lm
+
+# File extensions
+EXEEXT =
+
+# Pre-built configuration
+# See scripts/pnglibconf.mak for more options
+PNGLIBCONF_H_PREBUILT = scripts/pnglibconf.h.prebuilt
+
+# Variables
+OBJS =  png.o pngerror.o pngget.o pngmem.o pngpread.o \
+	pngread.o pngrio.o pngrtran.o pngrutil.o pngset.o \
+	pngtrans.o pngwio.o pngwrite.o pngwtran.o pngwutil.o
+
+# Targets
+all: static
+
+pnglibconf.h: $(PNGLIBCONF_H_PREBUILT)
+	$(CP) $(PNGLIBCONF_H_PREBUILT) $@
+
+.c.o:
+	$(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $<
+
+static: libpng.a pngtest$(EXEEXT)
+
+shared:
+	@echo This is a generic makefile that cannot create shared libraries.
+	@echo Please use a configuration that is specific to your platform.
+	@false
+
+libpng.a: $(OBJS)
+	$(AR_RC) $@ $(OBJS)
+	$(RANLIB) $@
+
+test: pngtest$(EXEEXT)
+	./pngtest$(EXEEXT)
+
+pngtest$(EXEEXT): pngtest.o libpng.a
+	$(LD) $(LDFLAGS) -o $@ pngtest.o libpng.a $(LIBS)
+
+clean:
+	$(RM_F) *.o libpng.a pngtest$(EXEEXT) pngout.png pnglibconf.h
+
+png.o:      png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngerror.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngget.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngmem.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngpread.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngread.o:  png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrio.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrtran.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrutil.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngset.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngtrans.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwio.o:   png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwrite.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwtran.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwutil.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+
+pngtest.o:  png.h pngconf.h pnglibconf.h
diff --git a/scripts/makefile.msys b/scripts/makefile.msys
index ade59b9..6b9daf8 100644
--- a/scripts/makefile.msys
+++ b/scripts/makefile.msys
@@ -1,10 +1,11 @@
 # makefile for libpng using MSYS/gcc (shared, static library)
+# Copyright (C) 2019 Cosmin Truta
 # Copyright (C) 2012 Glenn Randers-Pehrson and Christopher M. Wheeler
 #
-# Portions taken from makefile.linux:
+# Portions taken from makefile.linux and makefile.gcc:
+# Copyright (C) 2000 Cosmin Truta
 # Copyright (C) 1998, 1999, 2002, 2006, 2008, 2010-2014 Greg Roelofs and
 # Glenn Randers-Pehrson
-# Copyright (C) 2000 Cosmin Truta
 # Copyright (C) 1996, 1997 Andreas Dilger
 # Copyright (C) 1995 Guy Eric Schalnat, Group 42, Inc.
 #
@@ -176,7 +177,7 @@
 	./pngtest$(EXEEXT)
 
 pngtest$(EXEEXT): pngtest.o libpng.a
-	$(LD) $(LDFLAGS) -L$(ZLIBLIB) -o $@ pngtest.o libpng.a $(LIBS)
+	$(LD) $(LDFLAGS) -o $@ pngtest.o libpng.a $(LIBS)
 
 clean:
 	$(RM_F) *.o libpng.a pngtest$(EXEEXT) pngout.png pnglibconf.h $(LIBSO) \