This patch adds a machine_mode parameter to the TARGET_SIMD_CLONE_USABLE 
hook to enable rejecting SVE modes when the target architecture does not 
support SVE.

gcc/ChangeLog:

	* config/aarch64/aarch64.cc (aarch64_simd_clone_usable): Add mode
	parameter and use to to reject SVE modes when target architecture does
	not support SVE.
	* config/gcn/gcn.cc (gcn_simd_clone_usable): Add unused mode parameter.
	* config/i386/i386.cc (ix86_simd_clone_usable): Likewise.
	* doc/tm.texi (TARGET_SIMD_CLONE_USABLE): Document new parameter.
	* target.def (usable): Add new parameter.
	* tree-vect-stmts.cc (vectorizable_simd_clone_call): Pass vector mode
	to TARGET_SIMD_CLONE_CALL hook.