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/config.h.in b/src/config.h.in
index e13cc63..d1aaf70 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -258,6 +258,7 @@
 #undef HAVE_SYS_PARAM_H
 #undef HAVE_SYS_POLL_H
 #undef HAVE_SYS_PTEM_H
+#undef HAVE_SYS_PTMS_H
 #undef HAVE_SYS_RESOURCE_H
 #undef HAVE_SYS_SELECT_H
 #undef HAVE_SYS_STATFS_H