wasm cross-compiler doesn't compile with `+werror`
It appears that the Wasm backend isn't -Werror
clean. Specifically, this fails:
$ nix develop ghc.nix#devShells.x86_64-linux.wasi-cross
$ ./boot
$ configure_ghc
$ hadrian/build --flavour=default+werror
The first errors that are encountered are a number of RTS warnings.