Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Remove hacks to allow libkse to export its symbols in the LIBTHREAD_1_0
version namespace which was needed before the library version was
bumped.

WARNS=3'ify.

Repo copy libpthreads to libkse.
This introduces the WITHOUT_LIBKSE nob,
and changes WITHOUT_LIBPTHREADS to mean with neither threading libs.
Approved by: re(kensmith)

Add compatibility symbol maps. libpthread (.so.1 and .so.2)
used LIBTHREAD_1_0 as its version definition, but now needs
to define its symbols in the same namespace used by libc.
The compatibility hooks allows you to use libraries and
binaries built and linked to libpthread before libc was
built with symbol versioning. The shims can be removed if
libpthread is given a version bump.

Reviewed by: davidxu

Use PTHREAD_SCOPE_SYSTEM to decide what should be done.

Follow kernel change, restore signal mask correctly by using a command
of kse_thr_interrupt.

Add a wrapper for execve(). The exec'd process must be started with
the signal mask and pending signals of the calling thread. These
are stored in userland in libpthread.

There is a small race condition in this patch which could cause
problems if a signal arrives after setting the (kernel) signal
mask and before exec'ing. The thread's set of pending signals
also are not yet installed in the exec'd process. Both of these
will be corrected with the addition of a special syscall.

Reported & Tested by: Joost Bekkers <joost at jodocus dot org>
Reviewed by: julian, davidxu