vim-patch:8.0.0420: text garbled when the system encoding differs from 'encoding'

Problem:    When running :make the output may be in the system encoding,
            different from 'encoding'.
Solution:   Add the 'makeencoding' option. (Ken Takata)

2c7292dc5b

src/nvim/buffer_defs.h

@@ -637,6 +637,7 @@ struct file_buffer {
   uint32_t b_p_fex_flags;       ///< flags for 'formatexpr'
   char_u *b_p_kp;               ///< 'keywordprg'
   int b_p_lisp;                 ///< 'lisp'
+  char_u *b_p_menc;             ///< 'makeencoding'
   char_u *b_p_mps;              ///< 'matchpairs'
   int b_p_ml;                   ///< 'modeline'
   int b_p_ml_nobin;             ///< b_p_ml saved for binary mode