util: add an _unused_ macro and replace LIBINPUT_UNUSED

For annotating intentionally used variables it needs to be a bit
shorter, so let's replace the current one which was aimed at functions.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1184>

src/evdev-mt-touchpad.c

@@ -1912,7 +1912,7 @@ tp_handle_state(struct tp_dispatch *tp,
 	tp_3fg_drag_apply_config(tp->device);
 }
 
-LIBINPUT_UNUSED
+_unused_
 static inline void
 tp_debug_touch_state(struct tp_dispatch *tp,
 		     struct evdev_device *device)

src/evdev.c

@@ -1022,7 +1022,7 @@ evdev_read_switch_reliability_prop(struct evdev_device *device)
 	return r;
 }
 
-LIBINPUT_UNUSED
+_unused_
 static inline void
 evdev_print_event(struct evdev_device *device,
 		  const struct input_event *e)

src/libinput-util.h

@@ -70,7 +70,6 @@
 #define etrace(...) _trace(stderr, __VA_ARGS__)
 
 #define LIBINPUT_EXPORT __attribute__ ((visibility("default")))
-#define LIBINPUT_UNUSED __attribute__ ((unused))
 
 /* Commonly-used cleanup  */
 #ifdef udev_list_entry_foreach

src/libinput.c

@@ -3173,7 +3173,7 @@ switch_notify_toggle(struct libinput_device *device,
 #endif
 }
 
-LIBINPUT_UNUSED
+_unused_
 static inline void
 libinput_print_queued_event(struct libinput_event *event)
 {

src/util-macros.h

@@ -75,4 +75,5 @@
 #define CONCAT2(X,Y) X##Y
 #define CONCAT(X,Y) CONCAT2(X,Y)
 
+#define _unused_ __attribute__((unused))
 #define _fallthrough_ __attribute__((fallthrough))

test/litest.h

@@ -42,7 +42,7 @@
 
 #define START_TEST(func_)  \
    static enum litest_runner_result func_(const struct litest_runner_test_env *test_env) { \
-	int _i __attribute__((unused)) = test_env->rangeval;
+	int _i _unused_ = test_env->rangeval;
 
 #define END_TEST \
 	return LITEST_PASS; \