Added dockerfile for osx build

FROM debian:stretch

MAINTAINER Matteo De Carlo <matteo.dek@covolunablu.org>

# Install build tools

RUN apt-get update && \

    DEBIAN_FRONTEND=noninteractive apt-get upgrade -yy && \

    DEBIAN_FRONTEND=noninteractive apt-get install -yy \

        automake            \

        bison               \

        curl                \

        file                \

        flex                \

        git                 \

        libtool             \

        pkg-config          \

        python              \

        texinfo             \

        vim                 \

        gcc                 \

        g++                 \

        cmake               \

        wget

# Install osxcross

ENV OSXCROSS_SDK_VERSION 10.11

ENV MAKEFLAGS -j64

RUN mkdir /opt/osxcross &&                                      \

    cd /opt &&                                                  \

    git clone https://github.com/tpoechtrager/osxcross.git &&   \

    cd osxcross &&                                              \

    git checkout 474f359d2f27ff68916a064f0138c9188c63db7d &&    \

    ./tools/get_dependencies.sh &&                              \

    yes | INSTALLPREFIX=/usr ./build_clang.sh &&                \

    cd /opt/osxcross/build/llvm-3.9.1.src/build_stage2 && make install && \

    cd - && rm -rf /opt/osxcross/build && \

    curl -L -o ./tarballs/MacOSX${OSXCROSS_SDK_VERSION}.sdk.tar.xz \

         https://s3.amazonaws.com/andrew-osx-sdks/MacOSX${OSXCROSS_SDK_VERSION}.sdk.tar.xz && \

    yes | PORTABLE=true ./build.sh &&                           \

    ./build_compiler_rt.sh

## alternative SDK sources:

# https://s3.amazonaws.com/andrew-osx-sdks/MacOSX${OSXCROSS_SDK_VERSION}.sdk.tar.xz

# https://github.com/phracker/MacOSX-SDKs/releases/download/10.13/MacOSX${OSXCROSS_SDK_VERSION}.sdk.tar.xz

ENV PATH $PATH:/opt/osxcross/target/bin

CMD /bin/bash