Improving the Android build process, support different toolchains and Standard C++ library runtimes

[jwtowner]

Hi, I'd like to improve the build process for Android, including shell scripts, build files and patches to OpenSSL and Boost, to allow for more build variants wherein we can migrate towards using newer Android NDK toolchains, use Clang/LLVM toolchain to build OpenSSL, use libc++ instead of libstdc++, and so on.

Since Android NDK 15c is being bundled with the upcoming MSVS 2017 15.6 release, we'd like to be able to build against libc++ so that we can use C++14 language and library features not available with libstdc++ 4.8/4.9.

As part of this, I'd also like to make it possible to build the dependencies (OpenSSL, Boost) within the Windows Subsystem for Linux instead of a full standalone Linux system. Some of the shell scripts are currently incompatible with WSL due to stray carriage return line endings.

My current progress consists of having OpenSSL building with both GCC and Clang toolchains in Android NDKs 10 through 15, as well as OpenSSL 1.0.2k through 1.0.2n, using WSL as the build environment. I've removed the dependency on the setenv-android.sh shellscript and have rolled all of the environment setup directly into Build_android/openssl/Makefile.

I'm wondering if you'd be interested in accepting pull requests for this and if you'd like it all in one big patch or as multiple smaller patches?

[ras0219-msft]

Yes, I'd be happy to review changes in this direction!

I would prefer smaller patches when possible that each provide individual value. For example, please submit the changes to Boost separately from OpenSSL.

[jwtowner]

Got the go ahead from legal to sign the CLA. PR #662 improves how OpenSSL is built for Android, and is now ready for review. Thanks!

[jwtowner]

I've updated the build scripts and patches for building Boost on Android. Please see PR #711 for review. Thanks.

[jwtowner]

PR #714 is the last pull request for this feature, and I believe the final changes are in for the other PRs. I've tested cpprestsdk and dependencies built against Android NDK r15c using Clang 5 and the c++_static (libc++) runtime library, coupled with Xbox Live in a large scale game product for Android built in MSVS 2017 15.6.1. Everything seems to working working great.