patch 8.2.0149: maintaining a Vim9 branch separately is more work

Problem:    Maintaining a Vim9 branch separately is more work.
Solution:   Merge the Vim9 script changes.
diff --git a/src/macros.h b/src/macros.h
index 455705c..6631d4d 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -302,6 +302,10 @@
 # endif
 #endif
 
+#ifdef FEAT_EVAL
+# define FUNCARG(fp, j)	((char_u **)(fp->uf_args.ga_data))[j]
+#endif
+
 /*
  * In a hashtab item "hi_key" points to "di_key" in a dictitem.
  * This avoids adding a pointer to the hashtab item.