Enable firstprivate OpenACC reductions

Enable firstprivate OpenACC reductions

2018-09-05  Cesar Philippidis  <cesar@codesourcery.com>
	    Chung-Lin Tang  <cltang@codesourcery.com>

	gcc/
	* gimplify.c (omp_add_variable): Enable firstprivate reduction
	variables.

	gcc/testsuite/
	* c-c++-common/goacc/reduction-8.c: New test.

	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/privatize-reduction-1.c: New
	test.
	* testsuite/libgomp.oacc-c-c++-common/privatize-reduction-2.c: New
	test.

(cherry picked from openacc-gcc-9-branch commit
1add5113c32e7b8ea8536aee877f901a4a6eb5fc)