Make GN pass -target flags only on Android Clang

This fails on other configurations. The new behavior matches the GYP build.

R=scottmg@chromium.org
TBR=scottmg

Review URL: https://codereview.chromium.org/130923002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243930 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243930