tree-optimization/86270 - improve SSA coalescing for loop exit test

tree-optimization/86270 - improve SSA coalescing for loop exit test

The PR indicates a very specific issue with regard to SSA coalescing
failures because there's a pre IV increment loop exit test.  While
IVOPTs created the desired IL we later simplify the exit test into
the undesirable form again.  The following fixes this up during RTL
expansion where we try to improve coalescing of IVs.  That seems
easier that trying to avoid the simplification with some weird
heuristics (it could also have been written this way).

	PR tree-optimization/86270
	* tree-outof-ssa.cc (insert_backedge_copies): Pattern
	match a single conflict in a loop condition and adjust
	that avoiding the conflict if possible.

	* gcc.target/i386/pr86270.c: Adjust to check for no reg-reg
	copies as well.