Windows build

[Phil Longstaff]

I ran setup-ming64.ps1 -x86_64 $true -target_dir d:\gcdev64. It complained
about conflicts between msys2-runtime and catgets, but did seem to complete
successfully. It left me with instructions to start a MSys2/Mingw32 shell,
cd to my target directory, and run a jhbuild command. When I do this,
jhbuild returns almost immediately and seems to do nothing.

Is there more setup I need to do? I am somewhat familiar with the old
windows build system, but not the new one.

Thanks,
Phil