testsuite: Add vect_perm3_int guards

testsuite: Add vect_perm3_int guards

SLP vectorisation of gcc.dg/vect/fast-math-vect-call-1.c involves
a group of 3 floats, which requires the same permutation as
vect_perm3_int.

The load/store_lanes XFAILs in gcc.dg/vect/slp-perm-6.c implicitly
assumed vect_perm3_int, which is true for Advanced SIMD but not for
VLA SVE.  Whether it's true for fixed-length SVE depends on the
vector length.

The xfail selector applies on top of the target selector, so it's
not necessary to make the xfail selector a strict subset of the
target selector.

gcc/testsuite/
	* gcc.dg/vect/fast-math-vect-call-1.c: Only expect SLP to be used
	on vect_perm3_int targets.
	* gcc.dg/vect/slp-perm-6.c: Likewise.  Only XFAIL the LOAD/STORE_LANES
	tests on vect_perm3_int targets.