Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r261283:

Import libc++ 3.4 release. This contains a lot of bugfixes, and some
preliminary support for C++1y.

MFC r261604:

HEAD is not buildable for the past day. Commit a 'quick fix' in order to permit
buildworld to complete.

Reviewed by: theraven

MFC r261608:

Apply a cleaner solution for the sign warnings that can occur when
compiling libc++'s <locale> header with -Wsystem-headers on.

This has also been submitted upstream.

Reported by: asomers

MFC r261801:

An ABI incompatibility crept into the libc++ 3.4 import in r261283. It
was caused by upstream libc++ commit r194536, which aimed to make the
headers more standards-compliant, by making std::pair's copy constructor
trivial. Unfortunately, this could cause certain C++ applications using
shared libraries built against the previous version of libc++ to crash.

Fix the ABI incompatibility by making std::pair's copy constructor
non-trivial again.

Please note: Any C++ applications or shared libraries built with libc++
between r261283 and this revision should be recompiled.

Reported by: stefanf

MFC r253159 (by theraven):

Import new libcxxrt / libc++. This brings some bug fixes, including a
potential race condition for static initialisers.

MFC r246487 (by theraven):

Import new libc++ to head. Various small fixes and cleanups.

MFC r249998:

Merge libc++ trunk r180598. Contains several minor cleanups and bug
fixes, no major changes.

MFC r242945 (by theraven):

Import new version of libc++ into base.

MFC r241903:

Import libc++ trunk r165949. Among other improvements and bug fixes,
this has many visibility problems fixed, which should help with
compiling certain ports that exercise C++11 mode (i.e. Firefox).

Also, belatedly add the LICENSE.TXT and accompanying CREDITS.TXT files,
which are referred to in all the source files.

MFC r241907:

Fix two -Wsystem-header warnings in libc++ that were exposed by the new
ATF import. These have also been sent upstream.

Merged libcxxrt and libc++. Now available for testing on 9-stable with
-stdlib=libc++. Changes to libstdc++ not yet merged, so it is not yet possible
to mix libstdc++ and libc++ in the same program.

Merged revisions: 226702,226785,227006,227755,227983,227987,228531,228630,228761,229067,230127,232950,233098,234715-234716,234772

Import new version of libc++. Among other improvements, this comes with an
<atomic> header that works with clang 3.1 (and, importantly, the pre-3.1
snapshot currently in head)

Import a slightly newer libc++, with some bugs fixed that were found by running
the test suite on FreeBSD.

Approved by: dim (mentor)

Import new versions of libcxxrt and libc++.
Please tests any C++ code you care about with -stdlib=libc++!

Approved by: dim (mentor)

Import libc++ / libcxxrt into base. Not build by default yet (use
MK_LIBCPLUSPLUS=yes to enable). This is a work-in-progress. It works for
me, but is not guaranteed to work for anyone else and may eat your dog.

To build C++ using libc++, add -stdlib=libc++ to your CXX and LD flags.

Bug reports welcome, bug fixes even more welcome...

Approved by: dim (mentor)