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)
diff --git a/src/option.h b/src/option.h
index 62e66cd..2c6aeef 100644
--- a/src/option.h
+++ b/src/option.h
@@ -630,6 +630,9 @@
 EXTERN int	p_macatsui;	/* 'macatsui' */
 #endif
 EXTERN int	p_magic;	/* 'magic' */
+#ifdef FEAT_MBYTE
+EXTERN char_u	*p_menc;	/* 'makeencoding' */
+#endif
 #ifdef FEAT_QUICKFIX
 EXTERN char_u	*p_mef;		/* 'makeef' */
 EXTERN char_u	*p_mp;		/* 'makeprg' */
@@ -1065,6 +1068,9 @@
     , BV_LISP
     , BV_LW
 #endif
+#ifdef FEAT_MBYTE
+    , BV_MENC
+#endif
     , BV_MA
     , BV_ML
     , BV_MOD