Enable compiler docs testing in x86_64-gnu

Author: MaloJaffre

src/ci/docker/x86_64-gnu/Dockerfile

@@ -16,5 +16,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
-ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu --enable-sanitizers --enable-profiler
+ENV RUST_CONFIGURE_ARGS \
+ --build=x86_64-unknown-linux-gnu \
+ --enable-sanitizers \
+ --enable-profiler \
+ --enable-compiler-docs
 ENV SCRIPT python2.7 ../x.py test