- 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

Switch from 4-clause to 2-clause BSD license. (OpenBSD r1.22)
No functional change.

Obtained from: NetBSD via OpenBSD

Keep compatible parts in sync with OpenBSD v1.21, add some comments.
No functional changes.

Remove code #ifndef'ed in prev. commit to stay in sync with OpenBSD
v1.21 which just do that.

Be more GNU compatible:
don't be greedy on the GNU "::" extension when arg separated by whitespace
and POSIX_CORRECTLY is set. From POSIX point of view this is unclear
situation, so minimal assumption looks right.

Keep it sync with OpenBSD:
An optional argument cannot start with '-', even if permutation is
disabled.

Obtained from: OpenBSD getopt_long.c v1.17

Simplify one condition in prev. commit:
short_too already assumes FLAG_LONGONLY

Fix parsing of ambiguous options, whole loop must be processed

Make GNU-compatible following case:
single '-' in command line and '-' (non-first) in options

Make return code in noarg case GNU-compatible

Be more GNU-compatible in diagnostics

Improve GNU compatibility in several places, use internal GNU_COMPATIBLE
define for it.
Don't catch POSIXLY_CORRECT env. into static variable, it can be changed
on the fly by program.
Use P1003.2 standartized illoptchar[]

Change "-"-started options when POSIX_CORRECTLY is set handling
in favour of GNU instead of NetBSD, because configure's use us and
expect GNU.

Add getopt_long_only() from OpenBSD and other OpenBSD cleanups

PR: 63173
Submitted by: Marius Strobl <marius@alchemy.franken.de>

Unbreak the upgrade path from 4.9 after removal of GNU getopt and
<gnuregex.h>.

de-__P()

Add getopt_long(3).

Obtained from: NetBSD
Sponsored by: Apple