Android: Link c++abi and android_support when necessary

For older NDKs we used `__android_stl_lib` to link these libraries, but
the `CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED` code path does not use that.
Link the libraries the way the NDK toolchain file does:

  https://android.googlesource.com/platform/ndk/+/43b2de34ef9e3a70573fe51a9e069f985a4be5b9/build/cmake/android.toolchain.cmake#368
17 jobs for android-stl
Status Job ID Name Coverage
  External
passed cdash

passed ghostflow-check-master

passed ghostflow-stager

passed cdash

passed cdash

passed cdash

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager