PR libfortran/47571
	* acinclude.m4 (LIBGFOR_GTHREAD_WEAK): Remove.
	(LIBGFOR_CHECK_WEAKREF): New test.
	* configure.ac: Call LIBGFOR_CHECK_WEAKREF instead of
	LIBGFOR_GTHREAD_WEAK.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* intrinsics/system_clock.c: Use SUPPORTS_WEAKREF instead of
	SUPPORTS_WEAK and GTHREAD_USE_WEAK.

From-SVN: r227335