tree-optimization/118552 - failed LC SSA update after unrolling

When unrolling changes nesting relationship of loops we fail to
mark blocks as in need to change for LC SSA update.  Specifically
the LC SSA PHI on a former inner loop exit might be misplaced
if that loop becomes a sibling of its outer loop.

	PR tree-optimization/118552
	* cfgloopmanip.cc (fix_loop_placement): Properly mark
	exit source blocks as to be scanned for LC SSA update when
	the loops nesting relationship changed.
	(fix_loop_placements): Adjust.
	(fix_bb_placements): Likewise.

	* gcc.dg/torture/pr118552.c: New testcase.