Cygwin: utils: build with -Wimplicit-fallthrough=4 -Werror

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/utils/ssp.c

@@ -465,7 +465,7 @@ run_program (char *cmdline)
 		      thread_return_address[tix] = rv;
 		}
 	      set_step_threads (event.dwThreadId, stepping_enabled);
-	      /* fall-through */
+	      /*FALLTHRU*/
 	    case STATUS_SINGLE_STEP:
 	      opcode_count++;
 	      pc = (CONTEXT_REG)event.u.Exception.ExceptionRecord.ExceptionAddress;