modify Makefile so that tor-android can be compiled on MacOS

[cyBerta]

several build steps were failing.

• zlib was defaulting to libtool during the configure phase before compiling.

if "${CROSS_PREFIX}libtool" -V 2>&1 | grep Apple > /dev/null; then
            AR="${CROSS_PREFIX}libtool"
        elif libtool -V 2>&1 | grep Apple > /dev/null; then
            AR="libtool"
        else
            AR="/usr/bin/libtool"
        fi

However generating the resulting lib using that libtool failed (Maybe because that isn't the gnu libtool?). Setting the environment variables for AR to a libtool provided by the NDK as well as setting the CHOST allowed to overcome that issue.

• the wrong toolchain (linux-x86_64) was hardcoded and added to the path, which resulted in a subsequent build error
• the tor binary build failed since jni_md.h was missing. Adding the correct include path to the CPPFLAGS, fixed that.

[bitmold]

Thanks so much for figuring this out! I just also confirmed that everything still works fine on Linux after applying your changes