Enable LLVM assertions

Author: saethlin

src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile

@@ -77,6 +77,7 @@ ENV RUST_CONFIGURE_ARGS \
       --set target.x86_64-unknown-linux-gnu.ranlib=/rustroot/bin/llvm-ranlib \
       --set llvm.thin-lto=true \
       --set llvm.ninja=false \
+      --set llvm.assertions=true \
       --set rust.jemalloc \
       --set rust.use-lld=true
 ENV SCRIPT ../src/ci/pgo.sh python3 ../x.py dist \