Buildbot updates

* Add ZLIBWAPI_DLL and LEVELDB_DLL CMake options
* Remove legacy MINGWM10_DLL CMake option
* Update 32-bit buildbot (OpenAL updated, zlib updated)
* Change build directory for buildbots to '_build' to prevent removal of Android build files
* Use -win64 suffix for 64-bit Windows builds
* Fixes #1476