xwayland: Silence format-truncation compilation warnings

We are currently formatting 32-bit signed integers into 8 byte buffers,
which are too small, causing the compiler to complain. Update the buffer
size to the minimum required value of 12 bytes: 1 for the sign, 10 for
the number, and 1 for the null byte terminator.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>

compositor/xwayland.c

@@ -63,7 +63,7 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
 {
 	struct wet_xwayland *wxw = user_data;
 	pid_t pid;
-	char s[8], abstract_fd_str[8], unix_fd_str[8], wm_fd_str[8];
+	char s[12], abstract_fd_str[12], unix_fd_str[12], wm_fd_str[12];
 	int sv[2], wm[2], fd;
 	char *xserver = NULL;
 	struct weston_config *config = wet_get_config(wxw->compositor);