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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fsmonitor--daemon.c

@@ -1412,7 +1412,7 @@ done:
 	return err;
 }
 
-static int try_to_run_foreground_daemon(int detach_console)
+static int try_to_run_foreground_daemon(int detach_console MAYBE_UNUSED)
 {
 	/*
 	 * Technically, we don't need to probe for an existing daemon

fsmonitor-settings.c

@@ -62,7 +62,8 @@ static enum fsmonitor_reason check_remote(struct repository *r)
 }
 #endif
 
-static enum fsmonitor_reason check_for_incompatible(struct repository *r, int ipc)
+static enum fsmonitor_reason check_for_incompatible(struct repository *r,
+						    int ipc MAYBE_UNUSED)
 {
 	if (!r->worktree) {
 		/*