Move shared macros into skcms_internal.h.

This is another step on the road to separate translation units,
separating out shared code from skcms.cc.

Change-Id: Ibe08a3a88ddb141e0e7b519452bc07bdae8a1b2c
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/772601
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed