MFC r350360:

Merge libcxxrt master f96846efbfd508f66d91fcbbef5dd808947c7f6d.

Interesting fixes:
f96846e Fix std::size_t -> size_t to unbreak build against libc++ 6.0.0
6f4cfa2 Fix the uncaught exception count with rethrowing (PR 239265)
db54f53 Added C++14-specific operator delete (#47)

PR: 239265

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

Import libcxxrt master 516a65c109eb0a01e5e95fbef455eb3215135cef.

Interesting fixes:
3adaa2e Fix _Unwind_Exception cleanup functions
286776c Check exception cleanup function ptr before calling
edda626 Correct exception specifications on new and delete operators

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 new libcxxrt into vendor branch.

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.

Import new version of libcxxrt.

Approved by: dim (mentor)

Imported the latest version of libcxxrt.

Approved by: dim (mentor)

Import libcxxrt / libc++ into a vendor branch.

Approved by: dim (mentor)