Ensure GC-specific passes only run on GC modules

[tlively]

https://github.com/WebAssembly/binaryen/pull/4758 updated a bunch of GC-specific optimization passes to exit early if run on modules without GC enabled, but in the long run it might make more sense to add a mechanism to run those passes by default only on modules where they might be useful to avoid cluttering up the pass runner with useless passes.