Run RustPython with ThreadSanitizer

[threeifbyair]

I think there's a bug with threading, so I want to turn ThreadSanitizer on. Right now, this requires rebuilding std.

This is blocked by test_array falling over with a debug version of std -- and it appears that this is a real bug.

[threeifbyair]

To run:

TSAN_OPTIONS="suppressions=/home/abell/src/rp-testfuture/tsan.supp" RUSTFLAGS=“-Zsanitizer=thread” cargo run -Zbuild-std --target x86_64-unknown-linux-gnu — -m test