These are the patches that provide the ISO C 11 <threads.h> (except for
'thread_local').

The implementation is based on <pthread.h> for POSIX threads and on the
windows-* modules for native Windows. The only major headache was how to
work around the terrible AIX bugs.

The unit tests are adapted from the unit tests of 'thread', 'lock', 'cond',
'tls'.

16  threads-h: New module.
17  threads-h: Add tests.

This is just the header file.

18  thrd: New module.
19  mtx: New module.
20  cnd: New module.
21  tss: New module.
22  thrd: Add tests.
23  mtx: Add tests.
24  cnd: Add tests.
25  tss: Add tests.

These are the function implementations.

26  threads: New module.

This is just a convenience module that requests all of the function
implementations.