slp: Fix handling of IFN_CLZ/CTZ [PR112536]

We ICE on the following testcase now that IFN_C[LT]Z calls can have one or
two arguments (where 2 mean it is well defined at zero).
The following patch makes us create child node only for the first argument
and compatible_calls_p ensures the other argument is the same, which
at least according to the testcase seems sufficient because of vect
patterns.

2023-11-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/112536
	* tree-vect-slp.cc (arg0_map): New variable.
	(vect_get_operand_map): For IFN_CLZ or IFN_CTZ, return arg0_map.

	* gcc.dg/pr112536.c: New test.