external/freetype: Avoid duplicate zlib symbols

After 7229a380d3 "Update freetype to 2.12.0", my
--without-system-freetype --without-system-zlib Linux build started to fail to
link Library_skia with

> ld.lld: error: duplicate symbol: zlibVersion
> >>> defined at zutil.c:28 (workdir/UnpackedTarball/zlib/zutil.c:28)
> >>>            zutil.o:(zlibVersion) in archive core/workdir/LinkTarget/StaticLibrary/libzlib.a
> >>> defined at zutil.c:28 (src/gzip/zutil.c:28)
> >>>            ftgzip.o:(.text+0x0) in archive workdir/UnpackedTarball/freetype/instdir/lib/libfreetype.a

etc. because both those non-system libraries are provided as static archives.

There is also provisioning for symbol renaming in
workdir/UnpackedTarball/freetype/src/gzip/ftzconf.h via -DZ_PREFIX, so enable
that.  But three symbols were missing and would still produce linker failures,
so add them with external/freetype/zlib-duplicates.patch.

Change-Id: Ibe876d4e38e3e44ce00c64fb70c88fb0b1e3a910
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/142788
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

external/freetype/ExternalProject_freetype.mk

@@ -30,6 +30,7 @@ $(call gb_ExternalProject_get_state_target,freetype,build) :
 				$(call gb_ExternalProject_get_build_flags,freetype) \
 				$(gb_VISIBILITY_FLAGS) \
 				$(gb_EMSCRIPTEN_CPPFLAGS)" \
+			CPPFLAGS='$(CPPFLAGS) -DZ_PREFIX' \
 			LDFLAGS="$(call gb_ExternalProject_get_link_flags,freetype)" \
 		&& $(MAKE) install \
 		&& touch $@	)

external/freetype/UnpackedTarball_freetype.mk

@@ -14,6 +14,7 @@ $(eval $(call gb_UnpackedTarball_set_tarball,freetype,$(FREETYPE_TARBALL),,freet
 $(eval $(call gb_UnpackedTarball_add_patches,freetype,\
 	external/freetype/freetype-2.6.5.patch.1 \
 	external/freetype/ubsan.patch \
+	external/freetype/zlib-duplicates.patch \
 ))
 
 $(eval $(call gb_UnpackedTarball_set_patchlevel,freetype,0))

external/freetype/zlib-duplicates.patch

@@ -0,0 +1,22 @@
+--- src/gzip/ftzconf.h
++++ src/gzip/ftzconf.h
+@@ -130,10 +130,8 @@
+ #    define uncompress2           z_uncompress2
+ #  endif
+ #  define zError                z_zError
+-#  ifndef Z_SOLO
+ #    define zcalloc               z_zcalloc
+ #    define zcfree                z_zcfree
+-#  endif
+ #  define zlibCompileFlags      z_zlibCompileFlags
+ #  define zlibVersion           z_zlibVersion
+ 
+@@ -163,6 +161,8 @@
+ #  define gz_header_s           z_gz_header_s
+ #  define internal_state        z_internal_state
+ 
++#define z_errmsg z_z_errmsg
++
+ #endif
+ 
+ #if defined(__MSDOS__) && !defined(MSDOS)