gh-125842: Fix `sys.exit(0xffff_ffff)` on Windows (#125896)

gh-125842: Fix `sys.exit(0xffff_ffff)` on Windows (#125896)

On Windows, `long` is a signed 32-bit integer so it can't represent
`0xffff_ffff` without overflow. Windows exit codes are unsigned 32-bit
integers, so if a child process exits with `-1`, it will be represented
as `0xffff_ffff`.

Also fix a number of other possible cases where `_Py_HandleSystemExit`
could return with an exception set, leading to a `SystemError` (or
fatal error in debug builds) later on during shutdown.