match.pd: Fix fneg/fadd optimization [PR109583]

The following testcase ICEs on x86, foo function since my r14-22
improvement, but bar already since r13-4122.  The problem is the same,
in the if expression related_vector_mode is called and that starts with
  gcc_assert (VECTOR_MODE_P (vector_mode));
but nothing in the fneg/fadd match.pd pattern actually checks if the
VEC_PERM type has VECTOR_MODE_P (vec_mode).  In this case it has BLKmode
and so it ICEs.

The following patch makes sure we don't ICE on it.

2023-04-22  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/109583
	* match.pd (fneg/fadd simplify): Don't call related_vector_mode
	if vec_mode is not VECTOR_MODE_P.

	* gcc.dg/pr109583.c: New test.