mingw: Require Fedora
mingw: Require Fedora

Although it was never formally specified, it was always expected
that the mingw RPM build would happen on Fedora, if anything
because RHEL / CentOS don't ship the necessary mingw dependencies.

Make this fact explicit by erroring out if that's not the case,
the same way we already do in the main spec file.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

olafhering/libvirt,fabianfreyer/libvirt,eskultety/libvirt,eskultety/libvirt,jardasgit/libvirt,eskultety/libvirt,jfehlig/libvirt,olafhering/libvirt,jfehlig/libvirt,jardasgit/libvirt,nertpinx/libvirt,zippy2/libvirt,andreabolognani/libvirt,eskultety/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,libvirt/libvirt,jardasgit/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,crobinso/libvirt,olafhering/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,eskultety/libvirt,nertpinx/libvirt,nertpinx/libvirt,nertpinx/libvirt,zippy2/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,crobinso/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,libvirt/libvirt,libvirt/libvirt,olafhering/libvirt,andreabolognani/libvirt,jardasgit/libvirt,crobinso/libvirt,libvirt/libvirt