diff -u -r /home/fornwall/lib/android-ndk/sysroot/usr/include/pty.h ./usr/include/pty.h
--- /home/fornwall/lib/android-ndk/sysroot/usr/include/pty.h	2017-11-09 09:57:12.000000000 +0100
+++ ./usr/include/pty.h	2017-11-15 11:52:53.115077179 +0100
@@ -36,12 +36,9 @@
 
 __BEGIN_DECLS
 
-
-#if __ANDROID_API__ >= 23
-int openpty(int* __master_fd, int* __slave_fd, char* __slave_name, const struct termios* __termios_ptr, const struct winsize* __winsize_ptr) __INTRODUCED_IN(23);
-int forkpty(int* __master_fd, char* __slave_name, const struct termios* __termios_ptr, const struct winsize* __winsize_ptr) __INTRODUCED_IN(23);
-#endif /* __ANDROID_API__ >= 23 */
-
+/* In Termux these are implemented in the libutil package to support android-21. */
+int openpty(int* __master_fd, int* __slave_fd, char* __slave_name, const struct termios* __termios_ptr, const struct winsize* __winsize_ptr);
+int forkpty(int* __master_fd, char* __slave_name, const struct termios* __termios_ptr, const struct winsize* __winsize_ptr);
 
 __END_DECLS