libsa: Remove redundant sys/cdefs.h

Sponsored by: Netflix

stand: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

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

loader printf: Profile with TSLOG

Now that the loader tslog code doesn't call printf, we can profile
printf using TSLOG. On an EC2 c5.xlarge instance, we spend roughly
45 ms here (out of roughly 500 ms), presumably due to the time spent
writing output to the console.

MFC after: 1 week
Sponsored by: https://www.patreon.com/cperciva

loader: asprinf does crash arm64 due to missing NULL pointer check

PCHAR macro needs to check if d is NULL.

MFC after: 3 days

libsa: add asprintf()

asprintf() is a nice tool for string processing.

MFC after: 2 weeks

Make the v*printf() functions in libsa return int instead of void.
This makes them compatible with the C standard signatures, avoiding
spurious mismatch errors in the places where the oddball requirements
of standalone code end up putting two declarations of the same function
in play.

Add vsnprintf() to libsa. Alpha-sort the printf prototypes in stand.h.

I'm not sure why the v*printf() functions in libsa return void instead of
int, but this maintains that convention for the new function.

Move sys/boot to stand. Fix all references to new location

Sponsored by: Netflix