patch 8.2.1840: Vim9: error message is not clear about compilation error

Problem:    Vim9: error message is not clear about compilation error.
Solution:   Say "compiling" instead of "processing".
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 74be262..1dbea92 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -6715,6 +6715,7 @@
     int		called_emsg_before = called_emsg;
     int		ret = FAIL;
     sctx_T	save_current_sctx = current_sctx;
+    int		save_estack_compiling = estack_compiling;
     int		do_estack_push;
     int		emsg_before = called_emsg;
     int		new_def_function = FALSE;
@@ -6757,6 +6758,7 @@
     do_estack_push = !estack_top_is_ufunc(ufunc, 1);
     if (do_estack_push)
 	estack_push_ufunc(ufunc, 1);
+    estack_compiling = TRUE;
 
     if (ufunc->uf_def_args.ga_len > 0)
     {
@@ -7303,6 +7305,7 @@
     }
 
     current_sctx = save_current_sctx;
+    estack_compiling = save_estack_compiling;
     if (do_estack_push)
 	estack_pop();