Add static library build

This will be used in libvulkan_arm.so, to avoid a dependency on the
system shared library.

Also make the minizip and zlib targets static on the host.

Change-Id: I29bcd9e72ebb44cb3abe4a98fc111968b4bdfdb2
diff --git a/BUILD.gn b/BUILD.gn
index 6cef35a..d36590b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -36,9 +36,16 @@
   cflags = [ "-Wno-implicit-function-declaration" ]
 }
 
-shared_library("zlib") {
+target(default_library_type, "zlib") {
   output_name = "z"
+  deps = [
+    ":zlib_static",
+  ]
 
+  public_configs = [ ":zlib_config" ]
+}
+
+source_set("zlib_static") {
   sources = [
     "adler32.c",
     "compress.c",
@@ -84,7 +91,7 @@
   }
 }
 
-shared_library("minizip") {
+target(default_library_type, "minizip") {
   sources = [
     "contrib/minizip/crypt.h",
     "contrib/minizip/ioapi.c",