patch 8.1.2225: the "last used" info of a buffer is under used

Problem:    The "last used" info of a buffer is under used.
Solution:   Add "lastused" to getbufinfo(). List buffers sorted by last-used
            field. (Andi Massimino, closes #4722)
diff --git a/src/viminfo.c b/src/viminfo.c
index b162828..a49bb01 100644
--- a/src/viminfo.c
+++ b/src/viminfo.c
@@ -2152,7 +2152,7 @@
 /*
  * Compare functions for qsort() below, that compares b_last_used.
  */
-    static int
+    int
 buf_compare(const void *s1, const void *s2)
 {
     buf_T *buf1 = *(buf_T **)s1;