MFC r312466:

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

This implifies pathing in make/displayed output

Hoist all the mergeinfo up to the root in preparation for enforcing merges
to the root only. All MFC's were rerecorded to the root.

Going forward, if an MFC includes mergeinfo, it will need to be made to
the root and committed from the root. Merges with --ignore-ancestry
or diff | patch can go anywhere.

The mergeinfo in HEAD is in a bad state from years of neglect and manual
tampering and this was branched into 10.x. This confuses the coalescing
code and prevents it from doing its job.

Approved by: re (gjb, implicit)

MFC r258537, r258587:

r258537 (hrs):
Add ICONV_{GET,SET}_ILSEQ_INVALID iconvctl. GNU iconv returns
EILSEQ when there is an invalid character in the output codeset
while it is valid in the input. However, POSIX requires iconv()
to perform an implementation-defined conversion on the character.
So, Citrus iconv converts such a character to a special character
which means it is invalid in the output codeset.

This is not a problem in most cases but some software like libxml2
depends on GNU's behavior to determine if a character is output
as-is or another form such as a character entity (&#NNN;).

r258587 (peter):
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.

Approved by: re (kib)
Sponsored by: The FreeBSD Foundation

MFC r258283 - move iconv* symbols out of libc.so.7 namespace with
compatibility symbols to aid transition for existing 10.x installs.

Approved by: re (kib)

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