This unifies the behavior across the compiler and rest of ANGLE - for
example, one can use #define ANGLE_TEST_CONFIG to disable UNIMPLEMENTED
asserts in both the compiler and the rest of ANGLE. Compiler traces from
asserts also go to the same TRACE_OUTPUT_FILE as other traces instead of
being directed through ParseContext.

The compiler build already includes the common sources, so no changes to
build config are needed.

TEST=angle_unittests, angle_end2end_tests,
     dEQP-GLES3.functional.shaders.*
BUG=angleproject:983

Change-Id: Ifca4d16f667b1e5cf9c2e7cc4139940091917a1c
Reviewed-on: https://chromium-review.googlesource.com/266993Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>