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

Don't use _Unwind_Backtrace() on ARM as it's currently missing from our libgcc_s. andrew@ has patches to add it, so this can be reverted and sync'd with upstream later.

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

Merge libcxxrt c812a07cd2f95c1403baf0bbe0366e7618d1d6d3:

* Don't call the _fast version of the TLS accessor in terminate() or
unexpected().
1) TLS may not have been set up yet.
2) When we're in one of these functions, Really Bad Stuff has
happened and potentially saving a few cycles really isn't
important.
* Merge in fixes from FreeBSD trunk to make atomics work with recent
clang.

MFC after: 1 week

Fix a copy-and-paste error in libcxxrt.

Import new fix from libcxxrt. This fixes the case where you attempt to rethrow
an exception when you haven't caught one. This is largely a cosmetic fix, as
(unless you have a very unusual terminate handler installed) it will print a
nice error and then abort, rather than just aborting.

MFC after: 7 days

Merge new version of libcxxrt. This brings in three fixes:

- Don't treat pointers to members as pointers in catch blocks (they're usually
fat pointers).

- Correctly catch foreign exceptions in catchalls.

- Ensure that a happens-before relationship is established when setting
terminate handlers in one thread and calling them in another.

Import new version of libcxxrt. Now works correctly with libobjc2 to implement
the unified exception model for Objective-C++.

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)

Update libcxxrt to remove the pthread dependency.

Also add the license from upstream to contrib.

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)

libcxxrt version snapshot created.

Approved by: dim (mentor)

Import the new version of libcxxrt, which grew an extra ARM.

Approved by: dim (mentor)

Import libcxxrt / libc++ into a vendor branch.

Approved by: dim (mentor)