[libgomp, nvptx, --without-cuda-driver] Don't use system cuda driver

[libgomp, nvptx, --without-cuda-driver] Don't use system cuda driver

Using libgomp configure option --with-cuda-driver=<dir> we can indicate what
cuda driver to use to build the libgomp nvptx plugin.  Without such an option,
the system cuda driver is used, if available.  If not availabe, a dlopen
interface is used instead.

However, when we use --without-cuda-driver (or the equivalent
--with-cuda-driver=no) the system cuda driver is still used if available.

This patch fixes that, making sure that --without-cuda-driver selects the dlopen
interface.

Build on x86_64 with nvptx accelerator and tested libgomp testsuite, with and
without option --without-cuda-driver.

2018-08-04  Tom de Vries  <tdevries@suse.de>

	* plugin/configfrag.ac: For --without-cuda-driver, set
	CUDA_DRIVER_INCLUDE and CUDA_DRIVER_LIB to no.  Handle
	CUDA_DRIVER_INCLUDE == no and CUDA_DRIVER_LIB == no.
	* configure: Regenerate.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263310 138bc75d-0d04-0410-961f-82ee72b054a4