This patch adds a new target hook to enable us to adapt the types of 
return and parameters of simd clones.  We use this in two ways, the 
first one is to make sure we can create valid SVE types, including the 
SVE type attribute, when creating a SVE simd clone, even when the target 
options do not support SVE.  We are following the same behaviour seen 
with x86 that creates simd clones according to the ABI rules when no 
simdlen is provided, even if that simdlen is not supported by the 
current target options.  Note that this doesn't mean the simd clone will 
be used in auto-vectorization.

gcc/ChangeLog:

	(TARGET_SIMD_CLONE_ADJUST_RET_OR_PARAM): Define.
	* doc/tm.texi (TARGET_SIMD_CLONE_ADJUST_RET_OR_PARAM): Document.
	* doc/tm.texi.in (TARGET_SIMD_CLONE_ADJUST_RET_OR_PARAM): New.
	* omp-simd-clone.cc (simd_adjust_return_type): Call new hook.
	(simd_clone_adjust_argument_types): Likewise.
	* target.def (adjust_ret_or_param): New hook.
	* targhooks.cc (default_simd_clone_adjust_ret_or_param): New.
	* targhooks.h (default_simd_clone_adjust_ret_or_param): New.