This is needed short term to allow the test to pass when running on
Python 3.11 and later and avoid errors like
```
<stdin>:44:1: note: non-matching line after previous match is here
<string>:1: DeprecationWarning: 'pipes' is deprecated and slated for removal in Python 3.13
^
```
Long term we want to replace uses of the obsolete `pipes.quotes`
function with `shlex.quotes`.
Addresses rdar://109664710
It makes sense to just set this here since we aren't testing that functionality
and enables us to test this if we aren't using one of the specified Xcodes
(which can be useful).
Add three new flags, '--skip-clean-libdispatch', '--skip-clean-foundation', and
'--skip-clean-xctest', that leave the previous builds of those products in place.
Introduce a new parameter `--skip-llbuild-clean` to prevent this from
happening.
This mimicks similar logic in place for `swiftpm`, `swift-driver`
(#33563) and `xctest` (#19512)
Addresses rdar://75057069
