Address code review

Address code review.

Fixed issues raised in review

In D58985#1353091, @imp wrote:

So you are using the raw compiler commands, unconditionally. This will likely break gcc badly.
Normally we define 'standard' macros in cdefs.h and use those everywhere we can (eg, we'd use
them in clang, but maybe not gcc if there's no support for the concept). I don't have a good
design, but I can't see this not breaking things.

So that needs to be addressed before these can be committed.

In D58943#1352888, @markj wrote:

BTW, it is redundant to specify Fixes: and MFC-with:. Fixes: by itself is fine.