i3bar: work around weird clang compiler behavior

clang used to not warn (= error, with -Werror) about this line. Oh well.

Author: stapelberg

i3bar/src/xcb.c

@@ -1515,7 +1515,9 @@ static void send_tray_clientmessage(void) {
 static void init_tray(void) {
  DLOG("Initializing system tray functionality\n");
  /* request the tray manager atom for the X11 display we are running on */
- char atomname[strlen("_NET_SYSTEM_TRAY_S") + 11];
+ /* The following line cannot use strlen as that makes compilation fail with
+ * some versions of clang (-Wgnu-folding-constant): */
+ char atomname[18 /* strlen("_NET_SYSTEM_TRAY_S") */ + 11];
  snprintf(atomname, strlen("_NET_SYSTEM_TRAY_S") + 11, "_NET_SYSTEM_TRAY_S%d", screen);
  xcb_intern_atom_cookie_t tray_cookie;
  if (tray_reply == NULL) {