Fix missing gthr-default.h issue on separate libstdc++ configure
        * libstdc++-v3/acinclude.m4: Define glibcxx_thread_h.
        * libstdc++-v3/include/Makefile.am: Use glibcxx_thread_h.
        * libstdc++-v3/Makefile.in: Regenerate.
        * libstdc++-v3/configure: Regenerate.
        * libstdc++-v3/doc/Makefile.in: Regenerate.
        * libstdc++-v3/include/Makefile.in: Regenerate.
        * libstdc++-v3/libsupc++/Makefile.in: Regenerate.
        * libstdc++-v3/po/Makefile.in: Regenerate.
        * libstdc++-v3/python/Makefile.in: Regenerate.
        * libstdc++-v3/src/Makefile.in: Regenerate.
        * libstdc++-v3/src/c++11/Makefile.in: Regenerate.
        * libstdc++-v3/src/c++98/Makefile.in: Regenerate.
        * libstdc++-v3/testsuite/Makefile.in: Regenerate.

From-SVN: r192297