Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

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

MFC after: 2 weeks

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 after: 1 month

Vendor import of libc++ trunk r165949:
http://llvm.org/svn/llvm-project/libcxx/trunk@165949