tree-optimization/106198 - CFG cleanup vs LC SSA

tree-optimization/106198 - CFG cleanup vs LC SSA

This is another case like PR106182 where for the 2nd testcase in
the bug there are no removed or discovered loops but still changing
loop exits invalidates LC SSA and it is not enough to just scan for
uses in the blocks that changed loop depth.  One might argue that
if we'd include former exit destinations we'd pick up the original
LC SSA use but for virtuals on block merging we'd have propagated
those out (while for regular uses we insert copies).  CFG cleanup
can also be entered with loops needing fixup so any heuristics
based on loop structure are bound to fail.

	PR tree-optimization/106198
	* tree-cfgcleanup.cc (repair_loop_structures): Always do a
	full LC SSA rewrite but only if any blocks changed loop
	depth.

	* gcc.dg/pr106198.c: New testcase.