Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Add testing utility for behavior of atomic ops.

This small utility performs a sequence of atomic operations with random
parameters on an atomic variable. For every type, we also create 16
variables, to ensure that we test the correctness at different
alignments.

Switch over to gnu99 compilation on default for userland.

Tested by: make universe
Tested by: ports exp build (done by pav)
Reviewed by: ru
Reviewed by: silence on arch
Approved by: ed (mentor)

Start the dreaded NOFOO -> NO_FOO conversion.

OK'ed by: core

Switch over to a different, more flexible test output protocol that's
understood by Perl's Test::Harness module and prove(1) commands.

Update README to describe the new protocol. The work's broken down into
two main sets of changes.

First, update the existing test programs (shell scripts and C programs)
to produce output in the ok/not ok format, and to, where possible, also
produce a header describing the number of tests that are expected to be
run.

Second, provide the .t files that actually run the tests. In some cases
these are copies of, or very similar too, scripts that already existed.
I've kept the old scripts around so that it's possible to verify that
behaviour under this new system (in terms of whether or not a test fails)
is identical to the behaviour under the old system.

Add a TODO file.

For variables that are only checked with defined(), don't provide
any fake value.

Add a regression test for <tgmath.h>.