[CMake] How to refer to *.so files in Android NDK?

[Robert Dailey]

In my toolchain file for Android NDK, I specify the following *.so
paths manually:

set( ANDROID_PREBUILT_LIBRARIES
    ${CMAKE_ANDROID_NDK}/sources/cxx-stl/gnu-libstdc++/4.9/libs/x86/libgnustl_shared.so
    ${CMAKE_ANDROID_NDK}/platforms/android-15/arch-x86/usr/lib/libz.so
)

However, I'd like a better way to find these files: I already
configure CMake 3.8 using built-in Android support. It's able to
configure my toolchain just fine. Can I leverage some built-in
functionality to get the path to these files? I'm worried with the way
it is, if I change the other variables that the paths won't be valid
anymore and I'll have to update them manually again.