Use SIGUSR2 for vt switching instead of SIGUSR1

Xwayland uses SIGUSR1 to signal readiness.
With direct(-freebsd) session and Xwayland, wlroots was confusing the
Xwayland readiness signal with a vt switch signal, freezing the desktop.

Same problem was found in Weston in 2014:
https://phabricator.freedesktop.org/T7080

backend/session/direct-freebsd.c

@@ -148,8 +148,8 @@ static bool setup_tty(struct direct_session *session, struct wl_display *display
 
 	struct vt_mode mode = {
 		.mode = VT_PROCESS,
-		.relsig = SIGUSR1,
-		.acqsig = SIGUSR1,
+		.relsig = SIGUSR2,
+		.acqsig = SIGUSR2,
 		.frsig = SIGIO, // has to be set
 	};
 
@@ -159,7 +159,7 @@ static bool setup_tty(struct direct_session *session, struct wl_display *display
 	}
 
 	struct wl_event_loop *loop = wl_display_get_event_loop(display);
-	session->vt_source = wl_event_loop_add_signal(loop, SIGUSR1,
+	session->vt_source = wl_event_loop_add_signal(loop, SIGUSR2,
 		vt_handler, session);
 	if (!session->vt_source) {
 		goto error;

backend/session/direct.c

@@ -184,8 +184,8 @@ static bool setup_tty(struct direct_session *session, struct wl_display *display
 
 	struct vt_mode mode = {
 		.mode = VT_PROCESS,
-		.relsig = SIGUSR1,
-		.acqsig = SIGUSR1,
+		.relsig = SIGUSR2,
+		.acqsig = SIGUSR2,
 	};
 
 	if (ioctl(fd, VT_SETMODE, &mode) < 0) {
@@ -194,7 +194,7 @@ static bool setup_tty(struct direct_session *session, struct wl_display *display
 	}
 
 	struct wl_event_loop *loop = wl_display_get_event_loop(display);
-	session->vt_source = wl_event_loop_add_signal(loop, SIGUSR1,
+	session->vt_source = wl_event_loop_add_signal(loop, SIGUSR2,
 		vt_handler, session);
 	if (!session->vt_source) {
 		goto error;

xwayland/sockets.c

@@ -21,7 +21,9 @@
 static const char *lock_fmt = "/tmp/.X%d-lock";
 static const char *socket_dir = "/tmp/.X11-unix";
 static const char *socket_fmt = "/tmp/.X11-unix/X%d";
+#ifndef __linux__
 static const char *socket_fmt2 = "/tmp/.X11-unix/X%d_";
+#endif
 
 static int open_socket(struct sockaddr_un *addr, size_t path_size) {
 	int fd, rc;