Mark the exported entry points as stdcall. Because they may be returned as stdcall from eglGetProc address, the entry point functions must be stdcall. Fixes issues on 32-bit builds. BUG=angle:733 Change-Id: Ia20046a67fdc28c702837ec59b8299c6bb722006 Reviewed-on: https://chromium-review.googlesource.com/233471 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>