Auto merge of rust-lang#73383 - ecstatic-morse:test-unoptimized-std, r=Mark-Simulacrum

Run standard library unit tests without optimizations in `nopt` CI jobs

This was discussed in rust-lang#73288 as a way to catch similar issues in the future. This builds an unoptimized standard library with the bootstrap compiler and runs the unit tests. This takes about 2 minutes on my laptop.

I confirmed that this method works locally, although there may be a better way of implementing it. It would be better to use the stage 2 compiler instead of the bootstrap one.

Notably, there are currently four `libstd` unit tests that fail in debug mode on `i686-unkown-linux-gnu` (a tier one target):

```
failures:
    f32::tests::test_float_bits_conv
    f32::tests::test_total_cmp
    f64::tests::test_float_bits_conv
    f64::tests::test_total_cmp
```

These are the tests that prompted rust-lang#73288 as well as the ones added in rust-lang#72568, which is currently broken due to rust-lang#73328.

Author: bors

src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile

@@ -19,8 +19,13 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
+RUN mkdir -p /config
+RUN echo "[rust]" > /config/nopt-std-config.toml
+RUN echo "optimize = false" >> /config/nopt-std-config.toml
+
 ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu --disable-optimize-tests
-ENV SCRIPT python3 ../x.py --stage 2 test
+ENV SCRIPT python3 ../x.py test --stage 0 --config /config/nopt-std-config.toml library/std \
+  && python3 ../x.py --stage 2 test
 
 # FIXME(#59637) takes too long on CI right now
 ENV NO_LLVM_ASSERTIONS=1 NO_DEBUG_ASSERTIONS=1

src/ci/docker/host-x86_64/x86_64-gnu-nopt/Dockerfile

@@ -18,7 +18,12 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
+RUN mkdir -p /config
+RUN echo "[rust]" > /config/nopt-std-config.toml
+RUN echo "optimize = false" >> /config/nopt-std-config.toml
+
 ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu \
   --disable-optimize-tests \
   --set rust.test-compare-mode
-ENV SCRIPT python3 ../x.py --stage 2 test
+ENV SCRIPT python3 ../x.py test --stage 0 --config /config/nopt-std-config.toml library/std \
+  && python3 ../x.py --stage 2 test