Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r236695:

Fix two warnings about self-assignment in libc. These normally only
trigger with clang, when you either use -save-temps, or ccache.

Reported by: Sevan / Venture37 <venture37@gmail.com>

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

- Merge our local changes.
- Exclude unnecessary functions for us.