tree-optimization/100981 - fix SLP patterns involving reductions

tree-optimization/100981 - fix SLP patterns involving reductions

The following fixes the SLP FMA patterns to preserve reduction
info and the reduction vectorization to consider internal function
call defs for the reduction stmt.

2021-06-09  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/100981
gcc/
	* tree-vect-loop.c (vect_create_epilog_for_reduction): Use
	gimple_get_lhs to also handle calls.
	* tree-vect-slp-patterns.c (complex_pattern::build): Transfer
	reduction info.

gcc/testsuite/
	* gfortran.dg/vect/pr100981-1.f90: New testcase.

libgomp/
	* testsuite/libgomp.fortran/pr100981-2.f90: New testcase.