* lib/thrd.c: New file.
* m4/thrd.m4: New file.
* modules/thrd: New file.
* doc/posix-functions/thrd_current.texi: Mention the new module.
* doc/posix-functions/thrd_detach.texi: Likewise.
* doc/posix-functions/thrd_equal.texi: Likewise.
* doc/posix-functions/thrd_exit.texi: Likewise.
* doc/posix-functions/thrd_sleep.texi: Likewise.
* doc/posix-functions/thrd_yield.texi: Likewise.
* doc/posix-functions/thrd_create.texi: Mention the new module and the
AIX bug.
* doc/posix-functions/thrd_join.texi: Mention the new module and the
AIX and Solaris bugs.