unswitch: Fold case label lo/hi values to index type [PR105770]

The following testcase ICEs because we use different types in comparison,
idx has int type, while CASE_LOW has char type.

While I believe all CASE_{LOW,HIGH} in the same switch have to use the same
or compatible type, the index expression can have a promoted type as happens
in this testcase.  Other spots that handle switches do such foldings too.

2022-06-01  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/105770
	* tree-ssa-loop-unswitch.cc (find_unswitching_predicates_for_bb): Cast
	CASE_LOW and CASE_HIGH to TREE_TYPE (idx) before comparisons with idx.

	* gcc.dg/pr105770.c: New test.