use the same docker file for all architectures

.dockerignore

@@ -0,0 +1,2 @@
+*/
+!/Dockerfile

Dockerfile

@@ -0,0 +1,32 @@
+ARG img=debian/eol:wheezy
+FROM ${img}
+
+RUN uname -a
+
+ENV PATH=/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin:$PATH \
+    HOMEBREW_BUILD_BOTTLE=1 \
+    HOMEBREW_DEVELOPER=1 \
+    HOMEBREW_NO_ANALYTICS=1 \
+    HOMEBREW_NO_AUTO_UPDATE=1
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+      bzip2 \
+      ca-certificates \
+      curl \
+      file \
+      g++ \
+      git-core \
+      locales \
+      make \
+      patch \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN localedef -i en_US -f UTF-8 en_US.UTF-8 \
+    && useradd -m -s /bin/bash linuxbrew
+
+RUN git clone --depth=1 https://github.com/Homebrew/brew /home/linuxbrew/.linuxbrew/Homebrew \
+    && git clone --depth=1 https://github.com/Homebrew/linuxbrew-core /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-core \
+    && mkdir /home/linuxbrew/.linuxbrew/bin \
+    && ln -s ../Homebrew/bin/brew /home/linuxbrew/.linuxbrew/bin/ \
+    && brew tap homebrew/portable-ruby

README.md

@@ -16,9 +16,9 @@ Run `brew portable-package ruby` inside an OS X 10.9 VM (so it is compatible wit
 
 Build a Docker image for your architecture by running one of the following commands.
 
-- `docker build -f docker/Dockerfile.x86_64 -t homebrew-portable .`
-- `docker build -f docker/Dockerfile.arm -t homebrew-portable .`
-- `docker build -f docker/Dockerfile.arm64 -t homebrew-portable .`
+- `docker build -f Dockerfile --platform linux/amd64 --build-arg img=debian/eol:wheezy -t homebrew-portable .`
+- `docker build -f Dockerfile --platform linux/arm/v7 --build-arg img=debian/eol:wheezy -t homebrew-portable .`
+- `docker build -f Dockerfile --platform linux/arm64/v8 --build-arg img=debian/eol:jessie -t homebrew-portable .`
 
 Build the `portable-ruby` package using that Docker image.