Running is_clang.py is the current long-poll in `gn gen` time.
We can avoid it trivially in a few situations:
- We always use Clang on Android, iOS, and Mac.
- If cc and cxx are clang and clang++, it's Clang.
This cuts `gn gen` time from 80ms to 20ms on my laptop.
(Did you know gn has a --tracelog=trace.log option for creating Chrome-tracing-compatible traces? Pretty neat.)
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4746
Change-Id: Ic81d221675e8309cc9942bb9e62243d86658b02d
Reviewed-on: https://skia-review.googlesource.com/4746
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Ben Wagner <bungeman@google.com>
87c36f2302