Add libffi.map.in to extra dist files

Makefile.am

diff --git a/Makefile.am b/Makefile.am
index a4481df..e98cb34 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -21,7 +21,8 @@
 	 m4/ltversion.m4 src/debug.c msvcc.sh				\
 	generate-darwin-source-and-headers.py				\
 	libffi.xcodeproj/project.pbxproj				\
-	libtool-ldflags libtool-version configure.host README.md
+	libtool-ldflags libtool-version configure.host README.md        \
+	libffi.map.in
 
 # local.exp is generated by configure
 DISTCLEANFILES = local.exp