[PATCH 3/8] fsmonitor: mark some maybe-unused parameters

There's a bit of conditionally-compiled code in fsmonitor, so some function parameters may be unused depending on the build options:

  - in fsmonitor--daemon.c's try_to_run_foreground_daemon(), we take a
    detach_console argument, but it's only used on Windows. This seems
    intentional (and not mistakenly missing other platforms) based on
    the discussion in c284e27ba7 (fsmonitor--daemon: implement 'start'
    command, 2022-03-25), which introduced it.

  - in fsmonitor-setting.c's check_for_incompatible(), we pass the "ipc"
    flag down to the system-specific fsm_os__incompatible() helper. But
    we can only do so if our platform has such a helper.

In both cases we can mark the argument as MAYBE_UNUSED. That annotates it enough to suppress the compiler's -Wunused-parameter warning, but without making it impossible to use the variable, as a regular UNUSED annotation would.

Signed-off-by: Jeff King <peff@peff.net>
---
For a similar case in 2c3c3d88fc (imap-send: mark unused parameters with
NO_OPENSSL, 2023-08-29), I used the old:

  (void)some_parameter_that_might_not_be_used;

trick. But I realized while writing this one that MAYBE_UNUSED fits the bill a little more nicely, and I don't see any reason we would have portability problems with it.

 builtin/fsmonitor--daemon.c | 2 +-
 fsmonitor-settings.c        | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)