ParallelCompile: Enable worker on GL backend Except WGL AMD, WGL Intel, and GLX Nvidia. BUG=922936 Change-Id: I1bdbddd1485578465bcf6ece4b4b7173ae6f9f05 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1442312 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Jie A Chen <jie.a.chen@intel.com>