This will reduce binary size by a few kilobytes once we store mangled
names of functions as constexpr strings.

This still keeps mangled names human readable.

BUG=angleproject:2267
TEST=angle_unittests

Change-Id: Ia63980bd511c701a93e2c5e247d24578c7d7f332
Reviewed-on: https://chromium-review.googlesource.com/943101
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>