feat: use rustembedded/cross images and use static relocation model to fix cross-compile

cross/README.md

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+## Cross compilation
+
+The `cross` folder contains a set of convenience scripts (`build.sh` and `test.sh`) for cross-compiling Conduit.
+
+Currently supported targets are
+
+- aarch64-unknown-linux-musl
+- arm-unknown-linux-musleabihf
+- armv7-unknown-linux-musleabihf
+- x86\_64-unknown-linux-musl
+
+### Install prerequisites
+#### Docker
+[Installation guide](https://docs.docker.com/get-docker/).
+```sh
+$ sudo apt install docker
+$ sudo systemctl start docker
+$ sudo usermod -aG docker $USER
+$ newgrp docker
+```
+
+#### Cross
+[Installation guide](https://github.com/rust-embedded/cross/#installation).
+```sh
+$ cargo install cross
+```
+
+### Buiding Conduit
+```sh
+$ TARGET=armv7-unknown-linux-musleabihf ./cross/build.sh --release
+```
+The cross-compiled binary is at `target/armv7-unknown-linux-musleabihf/release/conduit`
+
+### Testing Conduit
+```sh
+$ TARGET=armv7-unknown-linux-musleabihf ./cross/test.sh --release
+```

cross/build.sh

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+#!/bin/bash
+set -ex
+
+# build custom container with libclang and static compilation
+tag="rust-cross:${TARGET:?}"
+docker build --tag="$tag" - << EOF
+FROM rustembedded/cross:$TARGET
+
+# Install libclang for generating bindings with rust-bindgen
+# The architecture is not relevant here since it's not used for compilation
+RUN apt-get update && \
+    apt-get install --assume-yes libclang-dev
+
+# Set the target prefix
+ENV TARGET_PREFIX="/usr/local/$(echo "${TARGET:?}" | sed -e 's/armv7/arm/' -e 's/-unknown//')"
+
+# Make sure that cc-rs links libc/libstdc++ statically when cross-compiling
+# See https://github.com/alexcrichton/cc-rs#external-configuration-via-environment-variables for more information
+ENV RUSTFLAGS="-L\$TARGET_PREFIX/lib" CXXSTDLIB="static=stdc++"
+# Forcefully linking against libatomic, libc and libgcc is required for arm32, otherwise symbols are missing
+$([[ $TARGET =~ arm ]] && echo 'ENV RUSTFLAGS="$RUSTFLAGS -Clink-arg=-lgcc -Clink-arg=-latomic -lstatic=c"')
+# Strip symbols while compiling in release mode
+$([[ $@ =~ -r ]] && echo 'ENV RUSTFLAGS="$RUSTFLAGS -Clink-arg=-s"')
+
+# Make sure that rust-bindgen uses the correct include path when cross-compiling
+# See https://github.com/rust-lang/rust-bindgen#environment-variables for more information
+ENV BINDGEN_EXTRA_CLANG_ARGS="-I\$TARGET_PREFIX/include"
+EOF
+
+# build conduit for a specific target
+cross build --target="$TARGET" $@

cross/test.sh

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+#!/usr/bin/env sh
+set -ex
+
+# Build conduit for a specific target
+cross/build.sh $@
+
+# Test conduit for a specific target
+cross test --target="$TARGET" $@