FunctionsGLX: add support for glXWaitX/GL The functions are not used in the code but are useful during development to try to see where race condition with the X server are. BUG=angleproject:892 Change-Id: Ie1267e46ac251bd9ac62e2a146db68ad84644fb8 Reviewed-on: https://chromium-review.googlesource.com/271177 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>