set the ANDROID_SDK_DIR, NDK and TOOLCHAIN vars only if unset. And don't add to PATH if already there
Update zlib from 1.2.7 to 1.2.8 becouse the 1.2.7 don't download
patch to solve other lconv decimal_point problem in cairo utils/cairo-trace/trace.c
In OSX MacPorts some glib-tools are placed in /opt/local/bin instead of /usr/local