vim-patch:8.1.1795: no syntax HL after splitting windows with :bufdo

Problem:    No syntax HL after splitting windows with :bufdo. (Yasuhiro
            Matsumoto)
Solution:   Trigger Syntax autocommands in buffers that are active.
            (closes vim/vim#4761)
c7f1e40021

src/nvim/buffer_defs.h

@@ -91,6 +91,7 @@ typedef struct {
 #define BF_READERR      0x40    // got errors while reading the file
 #define BF_DUMMY        0x80    // dummy buffer, only used internally
 #define BF_PRESERVED    0x100   // ":preserve" was used
+#define BF_SYN_SET      0x200   // 'syntax' option was set
 
 // Mask to check for flags that prevent normal writing
 #define BF_WRITE_MASK   (BF_NOTEDITED + BF_NEW + BF_READERR)