Fix building WITH_HEADLESS

An earlier commit removed the '#ifdef' check for the function call but not for
the function declaration.

source/creator/creator_signals.c

@@ -66,7 +66,6 @@ static void sig_handle_fpe(int UNUSED(sig))
 #  endif
 
 /* Handling `Ctrl-C` event in the console. */
-#  if !defined(WITH_HEADLESS)
 static void sig_handle_blender_esc(int sig)
 {
   G.is_break = true; /* forces render loop to read queue, not sure if its needed */
@@ -81,7 +80,6 @@ static void sig_handle_blender_esc(int sig)
     count++;
   }
 }
-#  endif
 
 static void sig_handle_crash_backtrace(FILE *fp)
 {