Add angle_code var to common.gypi and build_angle.gyp. Add GCC and clang warning flags from WebKit to ANGLE Mac and Linux builds.

The angle_code var differentiates between core ANGLE code vs. test code, sample code, and third party code.

Review URL: https://codereview.appspot.com/6427049/


git-svn-id: https://angleproject.googlecode.com/svn/trunk@1244 736b8ea6-26fd-11df-bfd4-992fa37f6226