the behavior previously found in the external setenv-android.sh
shell script, with the following numerous changes and additions to
allow for more varied build configurations:

- Added support for building with the Clang/LLVM toolchain instead
  of GCC to the Makefile.
- Added support for more recent Android NDK releases, including
  r10e, r11c, r12b, r13b, and r15c.
- Added support for the AArch64 Android target.
- Added support for more OpenSSL releases, with patch files for
  OpenSSL 1.0.2k through 1.0.2n and preliminary support for
  OpenSSL 1.1.0g to ensure forward compatibility.
- Most of the configuration variables in relation to Android now
  follow the same naming scheme and values as CMake.
- Exposed more configuration options as user overridable variables.
- The Makefile must now be invoked once per build target, it no
  longer builds libraries for both armv7 and x86. This simplifies
  the build rules in the Makefile.

The default build configuration for OpenSSL remains the same as
before, with GCC 4.8 as the toolchain, Android-18 as the API level
and OpenSSL 1.0.2k as the OpenSSL release. At a later date,
configure.sh can be updated with additional command line
options to further expose the new features.

This patch updates the OpenSSL Makefile and patches used for
Android builds so that it supports the unified headers and sysroot
found in newer Android NDKs since r14. This is required for Android
NDK r16 and later as the platform specific headers have been
removed. Additionally, the default prefix (install location) has
been changed in the Makefile to encode more variant information,
however the configure.sh script has been modified to override these
with the older defaults for the time being.