https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118530
--- Comment #1 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Clang-19 -fopenmp prints for this also an error:
foo.C:4:29: error: variant in '#pragma omp declare variant' with type
'<overloaded function type>' is incompatible with type 'void ()'
4 | #pragma omp declare variant(variant)
match(implementation={vendor("gnu")})
| ^~~~~~~
foo.C:10:5: note: in instantiation of function template specialization
'base<void>' requested here
10 | base<void>();
| ^
