diff -uNr sysroot.orig/usr/include/sys/cdefs.h sysroot/usr/include/sys/cdefs.h
--- sysroot.orig/usr/include/sys/cdefs.h	2019-02-12 16:12:24.000000000 +0000
+++ sysroot/usr/include/sys/cdefs.h	2019-03-20 13:27:29.977876824 +0000
@@ -336,3 +340,6 @@
 
 #include <android/versioning.h>
 #include <android/api-level.h>
+
+#define __TERMUX__ 1
+#define __TERMUX_PREFIX__ "@TERMUX_PREFIX@"