[vect]Account for epilogue's peeling for gaps when checking if we have enough

[vect]Account for epilogue's peeling for gaps when checking if we have enough
niters for epilogue

gcc/ChangeLog:
2019-11-11  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* tree-vect-loop-manip.c (vect_do_peeling): Take epilogue gaps into
	account when checking if there are enough iterations to vectorize
	epilogue.

gcc/testsuite/ChangeLog:
2019-11-11  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* gcc.dg/vect/vect-reduc-epilogue-gaps.c: New test.

From-SVN: r278049