Depends on #174659.
This PR adds a new map-type bit to control the fallback behavior when
when a pointer lookup fails.
For now, this is only meaningful with `RETURN_PARAM`, and can be used
for `need_device_ptr` (for which the default is to use `nullptr` as the
result
when lookup fails), and OpenMP 6.1's `use_device_ptr(fb_nullify)`.
Eventually, this can be extended to work with assumed-size maps on
`target`
constructs, to control what the argument should be set to when lookup
fails (the OpenMP spec does not have a way to control that yet).
Dependent PR: #170578.
3a9e3865b5