hadrian: Windows fixes (bindists, CI)

This commit implements a few Windows-specific fixes which get us from a CI
job that can't even get as far as starting the testsuite driver, to a state
where we can run the entire testssuite (but have test failures to fix).

- Don't forget about a potential extension for the haddock program, when
  preparing the bindist.
- Build the timeout program, used by the testsuite driver on Windows in place
  of the Python script used elsewhere, using the boot compiler. We could
  alternatively build it with the compiler that we're going to test but this
  would be a lot more tedious to write.
- Implement a wrapper-script less installation procedure for Windows, in
  `hadrian/bindist/Makefile.
- Make dependencies a bit more accurate in the aforementioned Makefile.
- Update Windows/Hadrian CI job accordingly.

This patch fixes #17486.