tree-optimization/109473 - ICE with reduction epilog adjustment op

tree-optimization/109473 - ICE with reduction epilog adjustment op

The following makes sure to carry out the reduction epilog adjustment
in the original computation type which for pointers is an unsigned
integer type.  There's a similar issue with signed vs. unsigned ops
and overflow which is fixed by this as well.

	PR tree-optimization/109473
	* tree-vect-loop.cc (vect_create_epilog_for_reduction):
	Convert scalar result to the computation type before performing
	the reduction adjustment.

	* gcc.dg/vect/pr109473.c: New testcase.