Return gthr-posix.h to libgcc (PR bootstrap/50982)

Return gthr-posix.h to libgcc (PR bootstrap/50982)

	libgcc:
	PR bootstrap/50982
	* config/gthr-posix.h: Move ...
	* gthr-posix.h: ... here.
	* config/gthr-lynx.h: Reflect this.
	* config/gthr-vxworks.h: Likewise.
	* config/rs6000/gthr-aix.h: Likewise.
	* configure.ac (target_thread_file): Likewise.
	* configure: Regenerate.

	libstdc++-v3:
	PR bootstrap/50982
	* include/Makefile.am (${host_builddir}/gthr-posix.h): Reflect
	gthr-posix.h move.
	* include/Makefile.in: Regenerate.

From-SVN: r181095