vim-patch:9.1.1396: 'grepformat' is a global option (#34060)

Problem:  The 'grepformat' option is global option, but it would be
          useful to have it buffer-local, similar to 'errorformat' and
          other quickfix related options (Dani Dickstein)
Solution: Add the necessary code to support global-local 'grepformat',
          allowing different buffers to parse different grep output
          formats (glepnir)

fixes: vim/vim#17316
closes: vim/vim#17315

7b9eb6389d

Co-authored-by: glepnir <glephunter@gmail.com>

src/nvim/buffer_defs.h

@@ -606,6 +606,7 @@ struct file_buffer {
   char *b_p_keymap;             ///< 'keymap'
 
   // local values for options which are normally global
+  char *b_p_gefm;               ///< 'grepformat' local value
   char *b_p_gp;                 ///< 'grepprg' local value
   char *b_p_mp;                 ///< 'makeprg' local value
   char *b_p_efm;                ///< 'errorformat' local value