vim-patch:8.0.1726: older MSVC doesn't support declarations halfway a block

Problem:    Older MSVC doesn't support declarations halfway a block.
Solution:   Move the declaration back to the start of the block.
df2c774ded

src/nvim/ex_docmd.c

@@ -6018,7 +6018,7 @@ static void ex_highlight(exarg_T *eap)
  */
 void not_exiting(void)
 {
-  exiting = FALSE;
+  exiting = false;
 }
 
 static bool before_quit_autocmds(win_T *wp, bool quit_all, int forceit)