fix internal libpng ppc(64el) build

by adding the missing files for VSX.

See https://lists.freedesktop.org/archives/libreoffice/2020-July/085564.html ff,

Change-Id: Ie368fcfa5cca80b2a7bd13be4add5d9973f3b05f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/99337
Tested-by: René Engelhard <rene@debian.org>
Tested-by: Jenkins
Reviewed-by: René Engelhard <rene@debian.org>
diff --git a/external/libpng/StaticLibrary_libpng.mk b/external/libpng/StaticLibrary_libpng.mk
index fe23641..2d56a27 100644
--- a/external/libpng/StaticLibrary_libpng.mk
+++ b/external/libpng/StaticLibrary_libpng.mk
@@ -38,6 +38,10 @@ $(eval $(call gb_StaticLibrary_add_generated_cobjects,libpng,\
	    UnpackedTarball/libpng/arm/filter_neon_intrinsics \
	    UnpackedTarball/libpng/arm/palette_neon_intrinsics \
	) \
	$(if $(filter POWERPC POWERPC64,$(CPUNAME)), \
	    UnpackedTarball/libpng/powerpc/powerpc_init \
	    UnpackedTarball/libpng/powerpc/filter_vsx_intrinsics \
	) \
))

# vim: set noet sw=4 ts=4: