[openacc] Move GOMP_OPENACC_DIM parsing out of nvptx plugin

[openacc] Move GOMP_OPENACC_DIM parsing out of nvptx plugin

2018-05-02  Tom de Vries  <tom@codesourcery.com>

	PR libgomp/85411
	* plugin/plugin-nvptx.c (nvptx_exec): Move parsing of
	GOMP_OPENACC_DIM ...
	* env.c (parse_gomp_openacc_dim): ... here.  New function.
	(initialize_env): Call parse_gomp_openacc_dim.
	(goacc_default_dims): Define.
	* libgomp.h (goacc_default_dims): Declare.
	* oacc-plugin.c (GOMP_PLUGIN_acc_default_dim): New function.
	* oacc-plugin.h (GOMP_PLUGIN_acc_default_dim): Declare.
	* libgomp.map: New version "GOMP_PLUGIN_1.2". Add
	GOMP_PLUGIN_acc_default_dim.
	* testsuite/libgomp.oacc-c-c++-common/loop-default-runtime.c: New test.
	* testsuite/libgomp.oacc-c-c++-common/loop-default.h: New test.

From-SVN: r259852