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)

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

META_MODE: Don't rebuild build-tools targets during normal build.

This avoids 'build command changed' due to CFLAGS/CC changes during the
normal build. Without this the build-tools targets end up rebuilding
for the *target* rather than keeping the native versions built in
build-tools.

Sponsored by: EMC / Isilon Storage Division

Properly fix these builds by adding NO_WMISSING_VARIABLE_DECLARATIONS from r249657.

This reverts r284374.

MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division

NO_WARNS when building for host

NO_MAN= has been deprecated in favor of MAN= for some time, go ahead
and finish the job. ncurses is now the only Makefile in the tree that
uses it since it wasn't a simple mechanical change, and will be
addressed in a future commit.

Add the BSD-licensed Citrus iconv to the base system with default off
setting. It can be built by setting the WITH_ICONV knob. While this
knob is unset, the library part, the binaries, the header file and
the metadata files will not be built or installed so it makes no impact
on the system if left turned off.

This work is based on the iconv implementation in NetBSD but a great
number of improvements and feature additions have been included:

- Some utilities have been added. There is a conversion table generator,
which can compare conversion tables to reference data generated by
GNU libiconv. This helps ensuring conversion compatibility.
- UTF-16 surrogate support and some endianness issues have been fixed.
- The rather chaotic Makefiles to build metadata have been refactored
and cleaned up, now it is easy to read and it is also easier to add
support for new encodings.
- A bunch of new encodings and encoding aliases have been added.
- Support for 1->2, 1->3 and 1->4 mappings, which is needed for
transliterating with flying accents as GNU does, like "u.
- Lots of warnings have been fixed, the major part of the code is
now WARNS=6 clean.
- New section 1 and section 5 manual pages have been added.
- Some GNU-specific calls have been implemented:
iconvlist(), iconvctl(), iconv_canonicalize(), iconv_open_into()
- Support for GNU's //IGNORE suffix has been added.
- The "-" argument for stdin is now recognized in iconv(1) as per POSIX.
- The Big5 conversion module has been fixed.
- The iconv.h header files is supposed to be compatible with the
GNU version, i.e. sources should build with base iconv.h and
GNU libiconv. It also includes a macro magic to deal with the
char ** and const char ** incompatibility.
- GNU compatibility: "" or "char" means the current local
encoding in use
- Various cleanups and style(9) fixes.

Approved by: delphij (mentor)
Obtained from: The NetBSD Project
Sponsored by: Google Summer of Code 2009