ipc: add LIBINPUT_CONFIG_ACCEL_PROFILE_CUSTOM entry

This was introduced in the last libinput release.

Fixes the following error:

    ../sway/ipc-json.c:928:17: error: enumeration value 'LIBINPUT_CONFIG_ACCEL_PROFILE_CUSTOM' not handled in switch [-Werror=switch]
      928 |                 switch (libinput_device_config_accel_get_profile(device)) {
          |                 ^~~~~~

meson.build

@@ -117,6 +117,11 @@ conf_data.set10('HAVE_LIBSYSTEMD', sdbus.found() and sdbus.name() == 'libsystemd
 conf_data.set10('HAVE_LIBELOGIND', sdbus.found() and sdbus.name() == 'libelogind')
 conf_data.set10('HAVE_BASU', sdbus.found() and sdbus.name() == 'basu')
 conf_data.set10('HAVE_TRAY', have_tray)
+conf_data.set10('HAVE_LIBINPUT_CONFIG_ACCEL_PROFILE_CUSTOM', cc.has_header_symbol(
+	'libinput.h',
+	'LIBINPUT_CONFIG_ACCEL_PROFILE_CUSTOM',
+	dependencies: libinput,
+))
 
 scdoc = dependency('scdoc', version: '>=1.9.2', native: true, required: get_option('man-pages'))
 if scdoc.found()

sway/ipc-json.c

@@ -935,6 +935,11 @@ static json_object *describe_libinput_device(struct libinput_device *device) {
 		case LIBINPUT_CONFIG_ACCEL_PROFILE_ADAPTIVE:
 			accel_profile = "adaptive";
 			break;
+#if HAVE_LIBINPUT_CONFIG_ACCEL_PROFILE_CUSTOM
+		case LIBINPUT_CONFIG_ACCEL_PROFILE_CUSTOM:
+			accel_profile = "custom";
+			break;
+#endif
 		}
 		json_object_object_add(object, "accel_profile",
 				json_object_new_string(accel_profile));