* config/threads-no.h: Remove file.
	* config/threads-posix.h: Remove file.

	* acconfig.h (_GLIBCPP_USE_THREADS): Remove.
	(_GLIBCPP_SUPPORTS_WEAK): Add (required by namespace-clean gthr*.h).
	(_GLIBCPP_HAVE_GTHR_DEFAULT): Likewise.
	* config.h.in: Regenerate.

	* acinclude.m4 (GLIBCPP_ENABLE_THREADS): Completely rework to
	setup and use gthr*.h files.  In particular, make gthr.h files
	namespace-clean in the staging area (they don't have to be for
	libgcc.a).
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	* src/Makefile.am (build_headers): Remove bits/c++threads.h
	and add bits/gthr.h bits/gthr-single.h bits/gthr-default.h.
	* src/Makefile.in: Regenerate.

	* include/bits/c++config: Cleanup threading configuration macros.
	In particular, define __STL_GTHREADS macro which controls...
	* include/bits/stl_threads.h: ...a brand new gthr.h-based
        configuration here.

	* config/c_io_stdio.h: Include staged gthr.h instead of local
	thread configuration file.  Always use __gthread_mutex_t
	instead of __mutext_type (or int).
	* include/bits/std_fstream.h: Likewise.

	* docs/html/17_intro/howto.html: Remove placeholder comment in
	case this configuration patch didn't make it.  Add advice that
	section only applies if configured with --enable-threads.
	* docs/html/23_containers/howto.html: Reword to make clear
	that _PTHREADS is no longer required for any port to be
	correctly using STL with threads.  Add advice that section
	only applies if configured with --enable-threads.

Co-Authored-By: John David Anglin <dave@hiauly1.hia.nrc.ca>

From-SVN: r42998