need pty.h on linux according to scott schwartz

src/cmd/9term/9term.h

diff --git a/src/cmd/9term/9term.h b/src/cmd/9term/9term.h
index 2453675..705648a 100644
--- a/src/cmd/9term/9term.h
+++ b/src/cmd/9term/9term.h
@@ -9,6 +9,10 @@
 #include <frame.h>
 #include <plumb.h>
 #include <termios.h>
+#include <sys/termios.h>
+#ifdef __linux__
+#include <pty.h>
+#endif
 
 #define fatal	sysfatal