This replaces the dlsyming of glX entry point with linking to libGL
which in trun allows the ANGLE to be traced using apitrace.

BUG=angleproject:892

Change-Id: Ic065582401e0e1e3fce1329cde216220a1e086a8
Reviewed-on: https://chromium-review.googlesource.com/286880Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>