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

Since contrib/libcxxrt's ancestry was never correct, subversion 1.8 and
higher cannot merge to it from the vendor area.

Re-bootstrap the ancestry by doing (apologies to your retinas):
* svn pg svn:mergeinfo contrib/libcxxrt > mergeinfo.txt
* svn rm contrib/libcxxrt
* svn cp ^/vendor/libcxxrt/dist@297299 contrib/libcxxrt
* svn rm CMakeLists.txt doxygen_config
* svn cp ^/head/contrib/libcxxrt/FREEBSD-upgrade@297299 contrib/libcxxrt
* svn cp ^/head/contrib/libcxxrt/exception.cc@297299 contrib/libcxxrt
* svn cp ^/head/contrib/libcxxrt/unwind-arm.h@297299 contrib/libcxxrt
* svn pd -R svn:mergeinfo contrib/libcxxrt
* svn ps -F mergeinfo.txt svn:mergeinfo contrib/libcxxrt

Import libcxxrt master 00bc29eb6513624824a6d7db2ebc768a4216a604.

Interesting fixes:
76584a0 Reorganize code to use only 32bit atomic ops for 32bit platforms
30d2ae5 Implement __cxa_throw_bad_array_new_length

Import new libcxxrt into vendor branch.

Import c812a07cd2f95c1403baf0bbe0366e7618d1d6d3 of libcxxrt:

* Fix a copy-and-paste error when setting the unexpected exception handler
(actually set the terminate handler by mistake).

* Fix some warnings.

Patch by Joerg Sonnenberger!

* 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.

Import b9db3a010143160624f123763025ab544b69bd9a 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.