MFC r241957:

MFC r241957:

  Fix several clang warnings in libstdc++, which were exposed by the
  recent atf import.  These changes are purely cosmetic, no functional
  change.

MFC r241959:

  Fix a number of other clang warnings in libstdc++, which could appear
  when building other C++ software with it.  Also fix one actual bug in
  libsupc++, which was exposed by such a warning.  This latter fix is the
  only functional change.

MFC r241960:

  For building GNU libstdc++ and libsupc++, filter out libc++-specific and
  -std= flags above c++98 or gnu++98 from CXXFLAGS *after* including
  bsd.lib.mk, otherwise some additions to CXXFLAGS done in bsd.*.mk might
  not be preserved.

git-svn-id: svn://svn.freebsd.org/base/stable/9@242347 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f