Revision 246368

MFC r246028 (by theraven):

  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 r246297:

  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>