GYP changes for FreeBSD and OpenBSD

third_party/libpng/libpng.gyp

Index: third_party/libpng/libpng.gyp
===================================================================
--- third_party/libpng/libpng.gyp	(revision 47284)
+++ third_party/libpng/libpng.gyp	(working copy)
@@ -5,10 +5,10 @@
 {
   'variables': {
     'conditions': [
-      [ 'OS=="linux"', {
+      [ 'OS=="linux" or OS=="freebsd" or OS=="openbsd"', {
         # Link to system .so since we already use it due to GTK.
         'use_system_libpng%': 1,
-      }, {  # OS!="linux"
+      }, {  # OS!="linux" and OS!="freebsd" and OS!="openbsd"
         'use_system_libpng%': 0,
       }],
     ],