Add angle_link_glx arg to standalone gn build. Port the angle_link_glx setting of the gyp build to the standalone gn build. When set to true, libGL will be linked into libANGLE, instead of dlopen-ed. This is useful when using apitrace. BUG=angleproject:1569 Change-Id: I16a91504960169efdcde3b2c50b944de148d9ba6 Reviewed-on: https://chromium-review.googlesource.com/821691 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Frank Henigman <fjhenigman@chromium.org>