Prerequisites for changing macro definitions in compiler_specific.h.

These tweaks will allow updating various macros to C++-standard style
attributes without having to simultaneously fix all callers.

Bug: none
Change-Id: Iea6bc753778aaffdbb345e6817938c33e5554c42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5806141
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Owners-Override: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1351531}
NOKEYCHECK=True
GitOrigin-RevId: 7bf5e3f9c4f3eeae614086abd9d0b8f528e2d3cb