Add cross compilation scripts

Dockerfile.build

@@ -0,0 +1,32 @@
+# this container is used for compiling dbmate against multiple targets
+FROM golang:1.5.1
+
+ENV CGO_ENABLED 1
+
+# i386 cross compilation
+RUN dpkg --add-architecture i386 && \
+	apt-get update && \
+	apt-get install -y libc6-dev-i386 && \
+	rm -rf /var/lib/apt/lists/*
+
+# osx cross compilation
+# ref: https://github.com/karalabe/xgo/blob/master/docker/base/Dockerfile
+ENV OSX_SDK_VERSION 10.9
+RUN cd /opt && \
+	git clone https://github.com/tpoechtrager/osxcross.git && \
+	cd osxcross && \
+	sed -i -e 's|-march=native||g' ./build_clang.sh ./wrapper/build.sh && \
+	apt-get update && \
+	./tools/get_dependencies.sh && \
+	rm -rf /var/lib/apt/lists/* && \
+	curl -fSL -o ./tarballs/MacOSX${OSX_SDK_VERSION}.sdk.tar.xz \
+		https://s3.amazonaws.com/andrew-osx-sdks/MacOSX${OSX_SDK_VERSION}.sdk.tar.xz && \
+	UNATTENDED=1 OSX_VERSION_MIN=10.6 ./build.sh
+ENV PATH /opt/osxcross/target/bin:$PATH
+
+# copy source files
+COPY . $GOPATH/src/github.com/adrianmacneil/dbmate
+WORKDIR $GOPATH/src/github.com/adrianmacneil/dbmate
+
+# fetch dependencies
+RUN go get -d -t -v