The Mingw32 toolchain is broadly obsoleted by the Mingw64 toolchain.
The latter has been adopted by Fedora 17 and newer. Maintaining a
RPM spec for Mingw32 is a needless burden, so switch to a Mingw64
RPM spec (which provides 32 & 64 bit builds).
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>