Update ANGLE's BUILD.gn to include definitions for GL_API.

Bug: skia:
Change-Id: I57a16af6c57166ead768ad73a8124690f1fa58e4
Reviewed-on: https://skia-review.googlesource.com/98302
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed