Fix GCC error on undeclared variable when not using abstract socket

This is a regression found by tinderbox in previous commit:

xcb_util.c: In function '_xcb_open':
xcb_util.c:213: error: 'fd' undeclared (first use in this function)

src/xcb_util.c

@@ -140,9 +140,7 @@ static int _xcb_open_abstract(char *protocol, const char *file, size_t filelen);
 
 static int _xcb_open(char *host, char *protocol, const int display)
 {
-#ifdef HAVE_ABSTRACT_SOCKETS
     int fd;
-#endif
     static const char unix_base[] = "/tmp/.X11-unix/X";
     const char *base = unix_base;
     size_t filelen;