To build this within the NDK several things have to be added in the jni
folder:

 - strongswan: The strongSwan sources.  This can either be an extracted tarball,
   or a symlink to the Git repository.  To build from the repository the sources
   have to be prepared first (see HACKING for a list of required tools):

     ./autogen.sh && ./configure && make && make distclean

 - openssl: The OpenSSL sources.  Since the sources need to be changed to be
   built on Android (and especially in the NDK), we provide a modified mirror
   of the official Android OpenSSL version on git.strongswan.org.

 - vstr: The Vstr string library.  Since cross-compiling this library is not
   that easy with the configure script and Makefiles included in the tarball,
   the easiest way to build it is using either droid-gcc (as described on
   wiki.strongswan.org) or a standalone toolchain built with the NDK.
   The build script provided on the wiki builds the library with droid-gcc
   and copies the required header files to the configured installation
   directory.  Please note that the Android.mk provided on the wiki (vstr.mk)
   does not work in the NDK.  A replacement is already in place in jni/vstr.