patch 8.2.2290: Vim9: unlet of global variable cannot be compiled

Problem:    Vim9: unlet of global variable cannot be compiled.
Solution:   Skip over variables that might be defined later. Give an error if
            a subscript is found. (closes #7585)
diff --git a/src/eval.c b/src/eval.c
index 87da4f3..75cbca9 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -813,9 +813,9 @@
     // Clear everything in "lp".
     CLEAR_POINTER(lp);
 
-    if (skip)
+    if (skip || (flags & GLV_COMPILING))
     {
-	// When skipping just find the end of the name.
+	// When skipping or compiling just find the end of the name.
 	lp->ll_name = name;
 	lp->ll_name_end = find_name_end(name, NULL, NULL,
 						      FNE_INCL_BR | fne_flags);