patch 7.4.2017

Problem:    When there are many errors adding them to the quickfix list takes
            a long time.
Solution:   Add BLN_NOOPT.  Don't call buf_valid() in buf_copy_options().
            Remember the last file name used.  When going through the buffer
            list start from the end of the list.  Only call buf_valid() when
            autocommands were executed.

src/vim.h

@@ -941,6 +941,7 @@ extern char *(*dyn_libintl_textdomain)(const char *domainname);
 #define BLN_LISTED	2	/* put new buffer in buffer list */
 #define BLN_DUMMY	4	/* allocating dummy buffer */
 #define BLN_NEW		8	/* create a new buffer */
+#define BLN_NOOPT	16	/* don't copy options to existing buffer */
 
 /* Values for in_cinkeys() */
 #define KEY_OPEN_FORW	0x101