Fixes problem where the glBlitFramebufferANGLE symbol couldn't be
found because Mesa's libGLESv2.so was being picked up.

BUG=angleproject:892

Change-Id: Ia3c55bd8eb3f078350adf4cc504bbbed6d97cb0b
Reviewed-on: https://chromium-review.googlesource.com/283950Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Kenneth Russell <kbr@chromium.org>