termios: add tcdrain

Change-Id: I05c0007f7bcc6ef5295c32f86fafbf1ad31e07fa
diff --git a/libc/include/termios.h b/libc/include/termios.h
index ad19089..0d44355 100644
--- a/libc/include/termios.h
+++ b/libc/include/termios.h
@@ -66,6 +66,11 @@
     return ioctl(fd, TCFLSH, (void *)(intptr_t)__queue);
 }
 
+static __inline__ int tcdrain(int fd)
+{
+    return ioctl(fd, TCSBRK, (void *)(intptr_t)1);
+}
+
 static __inline__ pid_t tcgetsid(int fd)
 {
     pid_t _pid;