electron-winstaller's Squirrel runs as 32-bit .NET but zips the package by
ShellExecuteEx-ing the 64-bit vendor/7z.exe. A 32-bit-only Wine prefix
('#arch=win32') cannot launch a 64-bit PE, so the cross-build fails with
'ShellExecuteEx failed: Bad EXE format'. Record the WINEARCH=win64 recipe
(and the pre-existing Wine+Mono requirement) instead of leaving it as a
build-host surprise.