This is a collateral patch from working on an update for the implementation status, namely on adding the TR14 (OpenMP 6.1) additions to https://gcc.gnu.org/onlinedocs/libgomp/OpenMP-Implementation-Status.html
Actually, I missed this feature myself - most of the time when calling API routines that take a device number as argument; '0' feels wrong – and 'omp_get_default_device()' is somewhat lengthy. In any case, this patch adds this extremely low hanging fruit. Comments before I commit it? Tobias PS: This only adds omp_default_device; the PR also mentions some cleanup tasks, but that's deferred to later.
