patch 8.0.0751: OpenPTY missing with some combination of features

Problem:    OpenPTY missing with some combination of features. (Kazunobu
            Kuriyama)
Solution:   Adjust #ifdef.  Also include pty.pro when needed.
diff --git a/src/proto.h b/src/proto.h
index b5a6224..92e3f60 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -212,15 +212,18 @@
 #  include "channel.pro"
 # endif
 
-# ifdef FEAT_GUI
-#  include "gui.pro"
+# if defined(FEAT_GUI) || defined(FEAT_JOB_CHANNEL)
 #  if defined(UNIX) || defined(MACOS)
 #   include "pty.pro"
 #  endif
+# endif
+
+# ifdef FEAT_GUI
+#  include "gui.pro"
 #  if !defined(HAVE_SETENV) && !defined(HAVE_PUTENV) && !defined(VMS)
-extern int putenv(const char *string);		/* from pty.c */
+extern int putenv(const char *string);			/* in misc2.c */
 #   ifdef USE_VIMPTY_GETENV
-extern char_u *vimpty_getenv(const char_u *string);	/* from pty.c */
+extern char_u *vimpty_getenv(const char_u *string);	/* in misc2.c */
 #   endif
 #  endif
 #  ifdef FEAT_GUI_W32