patch 9.0.0350: :echowindow does not work in a compiled function

Problem:    :echowindow does not work in a compiled function.
Solution:   Handle the expression at compile time.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index bf7390b..2036675 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -3251,10 +3251,13 @@
 
 	    case CMD_echo:
 	    case CMD_echon:
-	    case CMD_execute:
-	    case CMD_echomsg:
-	    case CMD_echoerr:
 	    case CMD_echoconsole:
+	    case CMD_echoerr:
+	    case CMD_echomsg:
+#ifdef HAS_MESSAGE_WINDOW
+	    case CMD_echowindow:
+#endif
+	    case CMD_execute:
 		    line = compile_mult_expr(p, ea.cmdidx, &cctx);
 		    break;