re-test x86_64_gnu, now that enzyme doesn't require llvm's plugin interface

Author: ZuseZ4

Diff for: src/ci/docker/host-x86_64/x86_64-gnu/Dockerfile

@@ -29,5 +29,6 @@ ENV RUST_CONFIGURE_ARGS \
  --enable-sanitizers \
  --enable-profiler \
  --enable-compiler-docs \
+ --set llvm.enzyme=true \
  --set llvm.libzstd=true
 ENV SCRIPT python3 ../x.py --stage 2 test