patch 8.1.0519: cannot save and restore the tag stack

Problem:    Cannot save and restore the tag stack.
Solution:   Add gettagstack() and settagstack(). (Yegappan Lakshmanan,
            closes #3604)
diff --git a/src/misc2.c b/src/misc2.c
index 3287f7e..ce69597 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -835,7 +835,7 @@
 #endif /* MEM_PROFILE */
 
 #ifdef FEAT_EVAL
-    static int
+    int
 alloc_does_fail(long_u size)
 {
     if (alloc_fail_countdown == 0)