Assertion failing when building `morello-purecap` on Morello

[kiancross]

When building on Morello for morello-purecap (and possibly for other targets - I haven't tested), the following error occurs:

Traceback (most recent call last):
  File "/home/kian/cheribuild/pycheribuild/__main__.py", line 365, in main
    run_and_kill_children_on_exit(real_main)
  File "/home/kian/cheribuild/pycheribuild/processutils.py", line 943, in run_and_kill_children_on_exit
    fn()
  File "/home/kian/cheribuild/pycheribuild/__main__.py", line 351, in real_main
    target.check_system_deps(cheri_config)
  File "/home/kian/cheribuild/pycheribuild/targets.py", line 132, in check_system_deps
    self._check_system_deps(config, self._get_or_create_project_no_setup(None, config, None))
  File "/home/kian/cheribuild/pycheribuild/targets.py", line 125, in _check_system_deps
    project.check_system_dependencies()
  File "/home/kian/cheribuild/pycheribuild/projects/build_qemu.py", line 160, in check_system_dependencies
    super().check_system_dependencies()
  File "/home/kian/cheribuild/pycheribuild/projects/project.py", line 617, in check_system_dependencies
    if self.make_args.command is None:
  File "/home/kian/cheribuild/pycheribuild/projects/project.py", line 221, in command
    cmd = self.__infer_command()
  File "/home/kian/cheribuild/pycheribuild/projects/project.py", line 242, in __infer_command
    self.__project.check_required_system_tool("gmake", homebrew="make")
  File "/home/kian/cheribuild/pycheribuild/projects/simple_project.py", line 1093, in check_required_system_tool
    assert instructions.fixit_hint() == existing.fixit_hint(), f"mismatched instructions for {executable}"
AssertionError: mismatched instructions for gmake
Fatal error: Unhandled exception: mismatched instructions for gmake

This is caused by the following assertion:

cheribuild/pycheribuild/projects/simple_project.py

Line 1078 in d8e86fc

assert instructions.fixit_hint() == existing.fixit_hint(), f"mismatched instructions for {executable}"

Inserting prints on the line before shows a comparison between Possibly running `pkg64 install gmake` fixes this. Note: package name may not be correct. and Possibly running `pkg64c install gmake` fixes this. Note: package name may not be correct., causing the assertion failure.

Commenting out the line above allows the build to proceed as expected.

@jrtc27 notes on Slack that the root cause is the line below: it is a class member, not an instance member, and as such, instances of SimpleProjectBase for hybrid and purecap builds share the same dict.

cheribuild/pycheribuild/projects/simple_project.py

Line 337 in d8e86fc

__checked_system_tools: "dict[str, InstallInstructions]" = {}

I'm leaving this as an issue rather than proposing a PR, as I'm not sure whether it is best to (1) turn the above assertion into a non-fatal warning or (2) fix the root cause as outlined above.