Hadrian: Use the Cabal build script on Windows by default
The Stack build script build.stack.bat currently fails on Windows
when invoked with the --configure flag, see:
The Cabal build script build.cabal.bat works reliably on my Windows
machine, so I am proposing to switch to it by default, that is, to run
it from the default build.bat script.
The Stack build script can still be run directly if need be.