libGLESv2_static and libGLESv2 can re-use the same object files.

BUG=angle:733

Change-Id: I894f4b5b6fbc1fc47812609d9e996691daf9f318
Reviewed-on: https://chromium-review.googlesource.com/214188Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>