Resolved shared library issues and expose C and C++ build tools

[philip-alldredge]

This pull request resolved #230. It removes the use of ndk-build and instead builds the shared library directly for the reasons described in that issue. In addition, it sets environment variables and generates a CMake toolchain based on the build targets and the min_sdk_version to allow crates which use the cc and cmake crates to build properly.

[philip-alldredge]

@mb64 tests are failing due to a docker issue. Will fix and push later tonight.

[philip-alldredge]

@mb64 all the issues have been resolved. The docker issue should be fixed as well. Tests are running. The docker issue was due to the rust docker image apparently defaulting to a new version of debian. We could stick with a version that uses the older version but I think we might as well build with the latest.

Once again, due to the number of commits, I recommend squashing once it is time to merge.

[philip-alldredge]

@mb64 tests failed so I"m looking into it.

[philip-alldredge]

@mb64 fixed it. Switched back to using stretch for docker image after all. Android SDK has compatibility issues with JDK 11.

[mb64]

Sorry for the delay – I've just finally gotten around to this again, and a few things caught my attention:

• I agree that Debian Stretch seems like the best/only solution to the JDK 8 requirement; JDK 11 removed the needed classes and Debian Buster removed JDK 8.
• Using clang removes support for older versions of the NDK. It might be worth finding out the minimum version and noting this somewhere.

No other issues with this have come up, so I'll merge.