Check ./x check bootstrap in pr-check-1

This check is relatively cheap, and is a quick way to root out breaking
check flow of `bootstrap` itself.

Author: jieyouxu

src/ci/docker/host-x86_64/pr-check-1/Dockerfile

@@ -40,6 +40,7 @@ COPY host-x86_64/pr-check-1/validate-toolstate.sh /scripts/
 # We disable optimized compiler built-ins because that requires a C toolchain for the target.
 # We also skip the x86_64-unknown-linux-gnu target as it is well-tested by other jobs.
 ENV SCRIPT \
+  python3 ../x.py check bootstrap && \
   /scripts/check-default-config-profiles.sh && \
   python3 ../x.py build src/tools/build-manifest && \
   python3 ../x.py test --stage 0 src/tools/compiletest && \