Technically, this patch is stand alone, but conceptually it based on the
submitted but not reviewed patch:
"[Patch] OpenMP: Support reverse offload (middle end part)"
https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598662.html

With that patch, for reverse offloads ('omp target device(ancestor:1)'),
calls like the following are added:
  GOMP_target_ext (-2 /* initial device */, omp_fn.1
where 'omp_fn.1' on nonhost devices a stub function just required for
looking up the host function pointer via the offload_funcs table.

The attached patch prepare for reverse-offload device->host
function-address lookup by requesting (if needed) the on-device address.

OK for mainline?

Tobias


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