Fix relocatable bindists for cross ghc and support bundling cross toolchain

https://gitlab.haskell.org/ghc/ghc/-/issues/26812

Improves developer experience by removing the need of configure & make install when installing ghc wasm backend. To keep compatibility with ghcup etc and avoid shipping both relocatable/non-relocatable bindists, we should only ship relocatable bindists that are still compatible with the old configure & make install workflow.