vect: Fix vect_get_smallest_scalar_type for simd clones

The vect_get_smallest_scalar_type helper function was using any argument to a
simd clone call when trying to determine the smallest scalar type that would be
vectorized.  This included the function pointer type in a MASK_CALL for
instance, and would result in the wrong type being selected.  Instead this
patch special cases simd_clone_call's and uses only scalar types of the
original function that get transformed into vector types.

gcc/ChangeLog:

	* tree-vect-data-refs.cc (vect_get_smallest_scalar_type): Special case
	simd clone calls and only use types that are mapped to vectors.
	(simd_clone_call_p): New helper function.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/vect-simd-clone-16f.c: Remove unnecessary differentation
	between targets with different pointer sizes.
	* gcc.dg/vect/vect-simd-clone-17f.c: Likewise.
	* gcc.dg/vect/vect-simd-clone-18f.c: Likewise.