[libgxps] build: Explicitly link to libpng

[Carlos Garcia Campos <carlosgc src gnome org>]

commit 883b607bf8a06f6e1b84d1c5967a6a90d60470a9
Author: Carlos Garcia Campos <carlosgc gnome org>
Date:   Thu Aug 13 17:18:08 2015 +0200

    build: Explicitly link to libpng
    
    Fix linking errors due to undefined libpng symbols in some cases.

 libgxps/Makefile.am |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/libgxps/Makefile.am b/libgxps/Makefile.am
index 8f633b9..3f65da1 100644
--- a/libgxps/Makefile.am
+++ b/libgxps/Makefile.am
@@ -61,6 +61,7 @@ libgxps_la_CFLAGS = \
        $(GXPS_CFLAGS)          \
        $(GXPS_DEBUG_CFLAGS)    \
        $(LCMS2_CFLAGS)         \
+       $(LIBPNG_CFLAGS)        \
        $(WARN_CFLAGS)          \
        $(AM_CFLAGS)
 
@@ -73,6 +74,7 @@ libgxps_la_LDFLAGS = \
 libgxps_la_LIBADD = \
        $(GXPS_LIBS)    \
        $(LCMS2_LIBS)   \
+       $(LIBPNG_LIBS)  \
        $(LIBJPEG)      \
        $(LIBTIFF)