patch 8.1.0824: SunOS/Solaris has a problem with ttys

Problem:    SunOS/Solaris has a problem with ttys.
Solution:   Add mch_isatty() with extra handling for SunOS. (Ozaki Kiichi,
            closes #3865)
diff --git a/src/proto/pty.pro b/src/proto/pty.pro
index 35e5c2b..52e20ef 100644
--- a/src/proto/pty.pro
+++ b/src/proto/pty.pro
@@ -1,4 +1,5 @@
 /* pty.c */
-int SetupSlavePTY(int fd);
-int OpenPTY(char **ttyn);
+int setup_slavepty(int fd);
+int mch_openpty(char **ttyn);
+int mch_isatty(int fd);
 /* vim: set ft=c : */