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

MFC r260553 (by theraven):

Add missing C++11 typeinfos to the libcxxrt version script.

PR: 185663

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

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

Add several missing symbols to libcxxrt's symbol version map, and remove
a few duplicates. This should fix building world with -stdlib=libc++
after r246028.

Submitted by: Yamaya Takashi <yamayan@kbh.biglobe.ne.jp>
MFC after: 1 week
X-MFC-With: r246028

Fix some symbol version mismatches between libstdc++ and libsupc++/libcxxrt
that were causing the runtime and STL libraries to see different versions of
various classes and functions when libstdc++ is used as a filter.

Note: This changes the ABI for libcxxrt, but libcxxrt is currently only in
-STABLE for testing and is not used by anything unless explicitly enabled by
the end user. No default compiler configurations use it.

libc++ will need to be recompiled after this change. make buildworld will do
this automatically, but make in lib/libc++ will not necessarily work unless the
new libcxxrt is installed first.

PR: kern/171610, stand/175453
Reviewed by: kib
MFC after: 1 week

Clean up some symbol versions for libsupc++ / libcxxrt.

MFC after: 1 week
Reviewed by: kan

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

Approved by: dim (mentor)

Add symbol versioning to libcxxrt.

Approved by: dim (mentor)