Add missing conversion in vect_create_epilog_for_reduction

Add missing conversion in vect_create_epilog_for_reduction

The direct_slp_reduc code in vect_create_epilog_for_reduction was
still assuming that all types involved in a reduction are the same
(up to types_compatible_p), whereas we now support differences in
sign.  This was causing an ICE in gcc.dg/vect/pr92324-4.c for SVE.

2019-12-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-loop.c (vect_create_epilog_for_reduction): When
	handling direct_slp_reduc, allow the PHI arguments to have
	a different type from the vector elements.

From-SVN: r279164