libc: split libc and syscall interposing (1/2)
System calls or their wrappers are now interposed by
libsys_interposing with purely libc entries remaining in
libc_interposing.
Use libsys_interposing_slot in libthr to update libsys_interposing,
but also make libc_interposing_slot fall back to
libsys_interposing_slot so an out of date libc has a chance of working
during updates.
Reviewed by: kib, emaste, imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/908