Enable GOMP_MAP_FIRSTPRIVATE_INT for OpenACC

Enable GOMP_MAP_FIRSTPRIVATE_INT for OpenACC

2018-12-22  Cesar Philippidis  <cesar@codesourcery.com>
            Julian Brown  <julian@codesourcery.com>
            Tobias Burnus  <tobias@codesourcery.com>

	gcc/
	* omp-low.cc (maybe_lookup_field_in_outer_ctx): New function.
	(convert_to_firstprivate_int): New function.
	(convert_from_firstprivate_int): New function.
	(lower_omp_target): Enable GOMP_MAP_FIRSTPRIVATE_INT in OpenACC.
	Remove unused variable.

	libgomp/
	* oacc-parallel.c (GOACC_parallel_keyed): Handle
	GOMP_MAP_FIRSTPRIVATE_INT host addresses.
	* plugin/plugin-nvptx.c (nvptx_exec): Handle
	GOMP_MAP_FIRSTPRIVATE_INT host addresses.
	* testsuite/libgomp.oacc-c++/firstprivate-int.C: New test.
	* testsuite/libgomp.oacc-c-c++-common/firstprivate-int.c: New
	test.
	* testsuite/libgomp.oacc-fortran/firstprivate-int.f90: New test.