Run codegen tests on a 32-bit target in PR CI

Author: saethlin

src/ci/docker/host-x86_64/pr-check-2/Dockerfile

@@ -30,6 +30,7 @@ ENV SCRIPT \
         python3 ../x.py check && \
         python3 ../x.py clippy ci --stage 2 && \
         python3 ../x.py test --stage 1 core alloc std test proc_macro && \
+        python3 ../x.py test --stage 1 tests/codegen-llvm --target wasm32-unknown-unknown && \
         python3 ../x.py test --stage 1 src/tools/compiletest && \
         python3 ../x.py doc bootstrap --stage 1 && \
         # Build both public and internal documentation.