[Android] Build fails for Android NDK r19

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When android.sh is executed on NDK r19, process fail with the following error.

WARNING:__main__:make_standalone_toolchain.py is no longer necessary. The
$NDK/toolchains/llvm/prebuilt/darwin-x86_64/bin directory contains target-specific scripts that perform
the same task. For example, instead of:

    $ python $NDK/build/tools/make_standalone_toolchain.py \
        --arch arm --api 24 --install-dir toolchain
    $ toolchain/bin/clang++ src.cpp

Instead use:

    $ $NDK/toolchains/llvm/prebuilt/darwin-x86_64/bin/armv7a-linux-androideabi24-clang++ src.cpp

[tanersener]

This is fixed in development branch. Issue will be closed when branch is merged to master.