Ok, found it. The value for CMAKE_ANDROID_STL_TYPE is the filename of one of
the .props files under:
"C:\Program Files (x86)\Microsoft Visual
Studio\2017\Professional\Common7\IDE\VC\VCTargets\Platforms\Tegra-Android\PlatformToolsets\Stl"
And LLVM is "llvm-libc++_shared" and
Ok, learning as I go along
The settings are documented here:
https://cmake.org/cmake/help/v3.12/prop_tgt/ANDROID_STL_TYPE.html#prop_tgt:ANDROID_STL_TYPE
which does not mention LLVM c++ library.
But the NVIDIA Tegra extension for Visual Studio can handle LLVM, as it is
settable in the
