tree-optimization/110310 - move vector epilogue disabling to analysis phase

tree-optimization/110310 - move vector epilogue disabling to analysis phase

The following removes late deciding to elide vectorized epilogues to
the analysis phase and also avoids altering the epilogues niter.
The costing part from vect_determine_partial_vectors_and_peeling is
moved to vect_analyze_loop_costing where we use the main loop
analysis to constrain the epilogue scalar iterations.

I have not tried to integrate this with vect_known_niters_smaller_than_vf.

It seems the for_epilogue_p parameter in
vect_determine_partial_vectors_and_peeling is largely useless and
we could compute that in the function itself.

	PR tree-optimization/110310
	* tree-vect-loop.cc (vect_determine_partial_vectors_and_peeling):
	Move costing part ...
	(vect_analyze_loop_costing): ... here.  Integrate better
	estimate for epilogues from ...
	(vect_analyze_loop_2): Call vect_determine_partial_vectors_and_peeling
	with actual epilogue status.
	* tree-vect-loop-manip.cc (vect_do_peeling): ... here and
	avoid cancelling epilogue vectorization.
	(vect_update_epilogue_niters): Remove.  No longer update
	epilogue LOOP_VINFO_NITERS.

	* gcc.target/i386/pr110310.c: New testcase.
	* gcc.dg/vect/slp-perm-12.c: Disable epilogue vectorization.