lib: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

libthr pshared: correct a bug in allocation

When __thr_pshared_offpage() is called for allocation, it must not use
the cached offpage for the key. Instead, the cached offpage must be
unmapped and removed from the cache, if any.

It is legitimate for the user code to unmap the shared lock object without
destroying it, and then mapping something over the freed VA to carry
another shared lock. In this case the cached offpage must be un-cached.

PR: 269277
Reported by: rau8344@gmail.com
Reviewed by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D38345

libthr: add pshared_destroy() helper

Rewviewed by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D38345

Remove PAGE_SIZE from libthr

In libthr we use PAGE_SIZE when allocating memory with mmap and to check
various structs will fit into a single page so we can use this allocator
for them.

Ask the kernel for the page size on init for use by the page allcator
and add a new machine dependent macro to hold the smallest page size
the architecture supports to check the structure is small enough.

This allows us to use the same libthr on arm64 with either 4k or 16k
pages.

Reviewed by: kib, markj, imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34984

Lock pshared_lock shared around fork, to ensure that the COW snapshot
of the pshared hash in child is consistent and can be safely used.

Reported and tested by: "Oleg V. Nauman" <oleg@opentransfer.com>
Sponsored by: The FreeBSD Foundation

Add two comments explaining the fine points of the hash
implementation.

Reviewed by: emaste
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D5490

Implement process-shared locks support for libthr.so.3, without
breaking the ABI. Special value is stored in the lock pointer to
indicate shared lock, and offline page in the shared memory is
allocated to store the actual lock.

Reviewed by: vangyzen (previous version)
Discussed with: deischen, emaste, jhb, rwatson,
Martin Simmons <martin@lispworks.com>
Tested by: pho
Sponsored by: The FreeBSD Foundation