Add cross cross-platform testing tools

Cross.toml

@@ -0,0 +1,5 @@
+[target.x86_64-unknown-linux-gnu]
+image = "local_cross:x86_64-unknown-linux-gnu"
+
+[target.powerpc64le-unknown-linux-gnu]
+image = "local_cross:powerpc64le-unknown-linux-gnu"

testing/cross/powerpc64le-unknown-linux-gnu.Dockerfile

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+FROM rustembedded/cross:powerpc64le-unknown-linux-gnu-0.2.1
+
+RUN dpkg --add-architecture powerpc64le && \
+    apt-get update && \
+    apt-get install --assume-yes libudev-dev
+
+RUN pkg-config --list-all && pkg-config --libs libudev && \
+    pkg-config --modversion libudev

testing/cross/x86_64-unknown-linux-gnu.Dockerfile

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+FROM rustembedded/cross:x86_64-unknown-linux-gnu-0.2.1
+
+RUN apt-get update && \
+    apt-get install --assume-yes libudev-dev
+
+RUN pkg-config --list-all && pkg-config --libs libudev && \
+    pkg-config --modversion libudev

testing/run_cross.sh

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+#!/bin/bash -xe
+
+pushd testing/cross/
+docker build -t local_cross:x86_64-unknown-linux-gnu -f x86_64-unknown-linux-gnu.Dockerfile .
+docker build -t local_cross:powerpc64le-unknown-linux-gnu -f powerpc64le-unknown-linux-gnu.Dockerfile .
+popd
+
+cross test --target x86_64-unknown-linux-gnu
+cross test --target x86_64-unknown-netbsd
+cross test --target powerpc64le-unknown-linux-gnu
+cross test --target x86_64-pc-windows-gnu