Use GL_APIENTRY and EGLAPIENTRY instead of __stdcall directly. BUG=angleproject:773 Change-Id: Iab098f787b966bf3999c22687af113cc9909593b Reviewed-on: https://chromium-review.googlesource.com/221796 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org> Tested-by: Kenneth Russell <kbr@chromium.org>