build src/ files independently

I wanted to see how tricky this would be to maintain,
to keep the possibility of non-unity builds alive.

Turns out, not too hard, especially with --include skcms.h.
I'm still kind of suspicious about the MSVC warning that
made us remove the relative includes in the first place, though.

This noted a few unused macros and functions in Transform.c that
were not warned about in the unity build.  That's all fixed up.

Change-Id: I1ed7acd008992246930ef6e6f12f0c42fc4fae87
Reviewed-on: https://skia-review.googlesource.com/102182
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed