Test with -Zmiri-provenance-gc=1 on Linux

Author: saethlin

src/ci/docker/host-x86_64/x86_64-gnu-tools/checktools.sh

@@ -25,7 +25,7 @@ cat /tmp/toolstate/toolstates.json
 python3 "$X_PY" test --stage 2 check-tools
 python3 "$X_PY" test --stage 2 src/tools/clippy
 python3 "$X_PY" test --stage 2 src/tools/rustfmt
-python3 "$X_PY" test --stage 2 src/tools/miri
+MIRIFLAGS=-Zmiri-provenance-gc=1 python3 "$X_PY" test --stage 2 src/tools/miri
 # We natively run this script on x86_64-unknown-linux-gnu and x86_64-pc-windows-msvc.
 # Also cover some other targets via cross-testing, in particular all tier 1 targets.
 export BOOTSTRAP_SKIP_TARGET_SANITY=1 # we don't need `cc` for these targets