Add tests for implied copy of variables in reduction clause.

Add tests for implied copy of variables in reduction clause.

The OpenACC reduction clause on compute construct implies a copy clause
for each reduction variable [1]. This patch adds tests to check if the
implied copy is being generated. The check covers various types and
operators as described in the specification.

[1] OpenACC 2.7 Specification section 2.5.13

gcc/testsuite/ChangeLog:

	* c-c++-common/goacc/implied-copy-1.c: New test.
	* c-c++-common/goacc/implied-copy-2.c: New test.
	* g++.dg/goacc/implied-copy.C: New test.
	* gcc.dg/goacc/implied-copy.c: New test.
	* gfortran.dg/goacc/implied-copy-1.f90: New test.
	* gfortran.dg/goacc/implied-copy-2.f90: New test.