[Bug libgomp/81378] New: [nvptx] Add openacc testcase using generated ptx but bypassing libgomp

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81378

            Bug ID: 81378
           Summary: [nvptx] Add openacc testcase using generated ptx but
                    bypassing libgomp
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

An openacc test-case uses libgomp and the libgomp nvptx plugin to offload ptx
code to a cuda device.

When reporting ptx bugs to nvidia, we send standalone test-cases that do not
use libgomp. These test-cases use a harness.c that, not surprisingly, contains
a lot of code from libgomp/plugin/plugin-nvptx.c.

It would be good to add harness.c to libgomp, factor out the common code into a
reusable form, and add a test-case that:
- compiles and runs an openacc test-case
- extracts the ptx
- uses the harness.c to compile and run the ptx, in the same way as the plugin
  would do