Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

libc_nonshared: Move to clibs package

Its needed by libc.a which lives in clibs.

PR: 254173

Use SRCTOP-relative paths to other directories instead of .CURDIR-relative ones

This implifies pathing in make/displayed output

MFC after: 3 weeks
Sponsored by: Dell EMC Isilon

Use src.opts.mk in preference to bsd.own.mk except where we need stuff
from the latter.

Spell NO_PROFILE= as MK_PROFILE=no.

Move the iconv wrapper source from libc_nonshared to libc/iconv so that
it is all in the one place again. Rename libc/iconv/iconv.c to
bsd_iconv.c. Compile the wrappers into libc.a so that WITHOUT_DYNAMICROOT
works again.

Discussed with: kib (and partly stolen from his patch)

Attempt to move the POSIX iconv* symbols out of runtime linker space.
FreeBSD systems usually implemented this as a third party module and
our implementation hasn't played as nicely with the old way as it could
have.

To that end:
* Rename the iconv* symbols in libc.so.7 to have a __bsd_ prefix.
* Provide .symver compatability with existing 10.x+ binaries that
referenced the iconv symbols. All existing binaries should work.
* Like on Linux/glibc systems, add a libc_nonshared.a to the ldscript
at /usr/lib/libc.so.
* Move the "iconv*" wrapper symbols to libc_nonshared.a

This should solve the runtime ambiguity about which symbols resolve
to where. If you compile against the iconv in libc, your runtime
dependencies will be unambiguous.

Old 9.x libraries and binaries will always resolve against their
libiconv.so.3 like they did on 9.x. They won't resolve against libc.

Old 10.x binaries will be satisified by the .symver helpers.

This should allow ports to selectively compile against the libiconv
port if needed and it should behave without ambiguity now.

Discussed with: kib