Split out target flags from $extra_cflags.

To compile particular TUs with Haswell- or Skylake-specific target
flags, we must be able to disambiguate the target-related flags
from the other flags like -O0 or -Dsomething.

Change-Id: Ia49a3969709a8ff26e55c28da58dbfcb5445c89a
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/777096
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
15 files changed