Commonly used Android toolchain files that pre-date CMake upstream
support may need to be updated to work with our new functionality.
They typically set CMAKE_SYSTEM_VERSION to 1, so detect that and
skip our upstream Android settings. When such toolchain files are
updated to account for our upstream support, they can then set
CMAKE_SYSTEM_VERSION to a valid Android API and get new behavior.
Commonly used Android toolchain files that pre-date CMake upstream
support use a few environment and CMake variables as search locations.
Use them too to aid transition.
Store the Android API level in CMAKE_SYSTEM_VERSION. If it is not
provided by the user, initialize it from CMAKE_ANDROID_API or fall back
to finding the latest available in the NDK.
Support for NVIDIA Nsight Tegra Visual Studio Edition was previously
implemented in the CMake VS IDE generators. Avoid interfering with
that functionality for now. Later we may try to integrate this.
