Notably:
- libc needs to #undef some of the macros from ssp/* for underlying
implementations
- ssp/* wants a __RENAME() macro (snatched more or less from NetBSD)
There's some extra hinkiness included for read(), since libc spells it
as "_read" while the rest of the world spells it "read."
Reviewed by: imp, ngie
Sponsored by: Stormshield
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D32307
