- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Make c99(1) invoke /usr/bin/cc with argv[0] set to "/usr/bin/cc" instead
of just "cc", since there is no reason to cause additional path searches
in this case.

MFC after: 3 days

Add missing static keywords to c99(1)

Sync program's usage() with manpage's SYNOPSIS.

Fix off-by-one error.

Re-add the code which maps POSIX standard library names into the ones
FreeBSD uses; f.e. -lpthread -> -pthread, -lxnet -> nothing.

Add the c99(1) utility, which is nothing more than a synonym for
cc -std=iso9899:1999 -pedantic, and is required by SUSv3.

PR; 36087