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/vim.h b/src/vim.h
index 917dbfa..230f5b3 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -811,6 +811,7 @@
 #define WILD_ALLLINKS		    0x200
 #define WILD_IGNORE_COMPLETESLASH   0x400
 #define WILD_NOERROR		    0x800  // sets EW_NOERROR
+#define WILD_BUFLASTUSED	    0x1000
 
 // Flags for expand_wildcards()
 #define EW_DIR		0x01	// include directory names