Make `gn gen` work on Windows again.

Clang detection is specific to GCC-like toolchains.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3171

Change-Id: I7144bc8e5cd3e774625b51a6dda981284ed1fdc1
Reviewed-on: https://skia-review.googlesource.com/3171
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed