MFC r315170:
r315170 (by imp):

Adopt SRCTOP in usr.bin

Prefer ${SRCTOP}/foo over ${.CURDIR}/../../foo and ${SRCTOP}/usr.bin/foo
over ${.CURDIR}/../foo for paths in Makefiles.

Silence on: arch@ (twice)

MFC r309364 r309367 r309624

locale: fix buffer management

Also, handle signed and unsigned chars, and more gracefully handle
invalid input.

locale: enable more warnings; fix them

Do not set WARNS, so it gets the current default of 6.
Fix the warnings by sprinkling static, const, or strdup.
Make some constant data tables const. Fix whitespace.

Sponsored by: Dell EMC

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

Always assign WARNS using ?=

- fix some nearby style bugs
- include Makefile.inc where it makes sense and reduces duplication

Approved by: ed (co-mentor)

Raise WARNS for various tools where possible.

Submitted by: Marius Nünnerich <marius@nuenneri.ch>

locale.c:

Use newly added __detect_path_locale() helper to lookup _PathLocale value.
It adds boundary checking for PATH_LOCALE environment variable value and
check for super-user fallback.

Makefile:

Add lib/libc/locale to compiler's include path (for setlocale.h)

Add WARNS

We have manpage now, so remove NOMAN

Add locale(1). I have used it for while as useful debugging tool
for locale related things. So, I think it could be useful for
others. It's not yet implement (or implement in different manner)
all POSIX things, but I think it's good enough for start.

POSIX conformance related updates and manpage to follow relatively soon.