libc: Teach libc about the BTI elf note

Add the Branch Target Identification (BTI) note to libc assembly
sources. As all obect files need the note for the library to have it
we need to insert it in all asm files.

Reviewed by: emaste, markj
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D42228

Remove $FreeBSD$: one-line .c pattern

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

libc: Fix longjmp/_longjmp(buf, 0) for AArch64 and RISC-V

These architectures fail to handle this special case, and will cause the
corresponding setjmp/_setjmp to return 0 rather than 1. Fix this and add
regression tests (also committed upstream).

PR: 268684
Reviewed by: arichardson, jhb
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D29363

Remove "All rights reserved" where I can in libc

These all have my copyright so can be removed. Some also have FreeBSD
Foundation copyright so drop from there as has been done for previous
files.

Sponsored by: The FreeBSD Foundation

Fix the comment showing the meaning of the first argument to sigprocmask.

Sponsored by: ABT Systems Ltd

Set the alignment of the setjmp magic values correctly. The alignment needs
to be before the lavel, otherwise an extra word may be added between the
label and the data.

Obtained from: ABT Systems Ltd
Sponsored by: The FReeBSD Foundation

Set the correct register when calling sigprocmask in longjmp.

Submitted by: Patrick Wildt <patrick@bitrig.org>
Obtained from: drahn@bitrig.org

Add the start of libc and libstand for arm64. Not all of the machine
dependent functions have been implemented, but this is enough for world.

Differential Revision: https://reviews.freebsd.org/D2132
Reviewed by: emaste
Sponsored by: The FreeBSD Foundation