so when we correctly detect mingw64 rather than mingw32 we actually
broke building of Gorm on mingw64. Additionally, examination of the
cases where we do differentiate between mingw32 and mingw64, in all but
one of them we do the same thing for both. That being the case, it
makes more sense to scrap the code to differentiate between the two
systems (except in the one case in target.make where we need to be aware
that the two systems prefix class names differently in the object
files), and adopt the triplet used by the mingw-w64 project (where os is
always mingw32 and we differentaiate 64bit windows using the vendor part
of the triplet) rather than the one returned by autoconf (config.guess).
