match.pd: Fix up gcc.dg/pr54346.c on i686-linux [PR54346]

match.pd: Fix up gcc.dg/pr54346.c on i686-linux [PR54346]

The pr54346.c testcase FAILs on i686-linux (without -msse*) for multiple
reasons.  One is the trivial missing -Wno-psabi which the following patch
adds, but that isn't enough.  The thing is that without native vector
support, we have VEC_PERM_EXPRs in the IL and are actually considering
the nested VEC_PERM_EXPRs into one VEC_PERM_EXPR optimization, but punt
because can_vec_perm_const_p (result_mode, op_mode, sel2, false) is false.

Such a test makes sense to prevent "optimizing" two VEC_PERM_EXPRs
that can be handled by the backend natively into one VEC_PERM_EXPR
that can't be handled.  But if both of the original VEC_PERM_EXPRs
can't be handled natively either, having just one VEC_PERM_EXPR that will be
lowered by generic vec lowering is IMHO still better than 2.
Or even if we trade just one VEC_PERM_EXPR that can't be handled plus
one that can to one that can't be handled.

Also, removing the testcase's executable permissions...

2022-10-21  <jakub@redhat.com>

	PR tree-optimization/54346
	* match.pd ((vec_perm (vec_perm@0 @1 @2 VECTOR_CST) @0 VECTOR_CST)):
	Optimize nested VEC_PERM_EXPRs even if target can't handle the
	new one provided we don't increase number of VEC_PERM_EXPRs the
	target can't handle.

	* gcc.dg/pr54346.c: Add -Wno-psabi to dg-options.