Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Use umtx to implement process sharable semaphore, to make this work,
now type sema_t is a structure which can be put in a shared memory area,
and multiple processes can operate it concurrently.
User can either use mmap(MAP_SHARED) + sem_init(pshared=1) or use sem_open()
to initialize a shared semaphore.
Named semaphore uses file system and is located in /tmp directory, and its
file name is prefixed with 'SEMD', so now it is chroot or jail friendly.
In simplist cases, both for named and un-named semaphore, userland code
does not have to enter kernel to reduce/increase semaphore's count.
The semaphore is designed to be crash-safe, it means even if an application
is crashed in the middle of operating semaphore, the semaphore state is
still safely recovered by later use, there is no waiter counter maintained
by userland code.
The main semaphore code is in libc and libthr only has some necessary stubs,
this makes it possible that a non-threaded application can use semaphore
without linking to thread library.
Old semaphore implementation is kept libc to maintain binary compatibility.
The kernel ksem API is no longer used in the new implemenation.

Discussed on: threads@

Forced commit to note that these files have been repo-copied from
src/sys/posix4/.

Repo-copy done by: kuriyama

Const-qualify ksem_timedwait's parameter abstime as it's only passed in.

/* -> /*- for license, minor formatting changes

The sem_timedwait() and ksem_timedwait() functions both
need struct timespec, so define it here.

Discussed in: standards (wollman)

Add ksem_timedwait() to complement ksem_wait().

Glanced at by: alfred

Add the rest of the kernel support for the sem_ API in kern/uipc_sem.c.

Option 'P1003_1B_SEMAPHORES' to compile them in, or load the "sem" module
to activate them.

Have kern/makesyscalls.sh emit an include for sys/_semaphore.h into sysproto.h
to pull in the typedef for semid_t.

Add the syscalls to the syscall table as module stubs.