Bug 1371266 - libpng should be built with -std=c89. r=glennrp

media/libpng/moz.build

@@ -64,3 +64,6 @@ FINAL_LIBRARY = 'gkmedias'
 
 # We allow warnings for third-party code that can be updated from upstream.
 ALLOW_COMPILER_WARNINGS = True
+
+if CONFIG['GNU_CC']:
+    CFLAGS += ['-std=c89']

mozilla-config.h.in

@@ -13,7 +13,7 @@
 #endif
 #endif
 
-// Expands to all the defines from configure.
+/* Expands to all the defines from configure. */
 #undef ALLDEFINES
 
 /*