Add in powerpc cross compilation tools

Docker/Dockerfile.cross-compiler

@@ -3,7 +3,7 @@ FROM $DOCKER_BASE_IMAGE
 
 USER root
 
-ARG DEPS_TESTING="gcc-arm-linux-gnueabi gcc-arm-linux-gnueabihf gcc-aarch64-linux-gnu"
+ARG DEPS_TESTING="gcc-arm-linux-gnueabi gcc-arm-linux-gnueabihf gcc-aarch64-linux-gnu gcc-powerpc-linux-gnu gcc-powerpc64-linux-gnu"
 RUN DEBIAN_FRONTEND=noninteractive apt update \
                     && apt install -y ${DEPS_TESTING} \
                     && apt clean -y && rm -rf /var/lib/apt/lists/*