re PR target/51957 (ppc64 .debug_loc toc reference)

re PR target/51957 (ppc64 .debug_loc toc reference)

	PR target/51957
	* target.def (const_not_ok_for_debug_p): New hook.
	* doc/tm.texi.in (TARGET_CONST_NOT_OK_FOR_DEBUG_P): New hook
	documentation.
	* doc/tm.texi: Regenerated.
	* dwarf2out.c (const_ok_for_output_1): If
	targetm.const_not_ok_for_debug_p returns true, fail.
	* config/rs6000/rs6000.c (rs6000_const_not_ok_for_debug_p): New
	function.
	(TARGET_CONST_NOT_OK_FOR_DEBUG_P): Redefine.

	* gcc.dg/pr51957-1.c: New test.
	* gcc.dg/pr51957-1.h: New file.
	* gcc.dg/pr51957-2.c: New test.

From-SVN: r183468