Fix Android skdiff build
Fix Android skdiff build

Problem: we use one set of GYP_DEFINES for all of the builds in
the Android buildbots.  But, when we build skdiff, we're building
for Linux, not Android, so this isn't valid.


TBR: epoger@

git-svn-id: 32fc27f4dcfb6c0385cd9719852b95fe6680452d@5445 2bbb7eff-a529-9590-31e7-b0007b416f81

google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot