Enable setting vector length using -fopenacc-dim, f.i. -fopenacc-dim=::128.

2019-01-12  Tom de Vries  <tdevries@suse.de>

	* config/nvptx/nvptx.c (nvptx_goacc_validate_dims_1): Alow setting
	vector length using -fopenacc-dim.

	* plugin/plugin-nvptx.c (nvptx_exec): Update error message.

From-SVN: r267896