Make a rule merging test specifically for this repository

[hjorthjort]

Relying on the unit tests in wasm-semantics means relying on the test embedding there (with assert_return, etc.), which we don't want to.

Make a simple module:

(module
   (func $main 
      .... ;; body
   )
   (start $main)
)

and merge the rules of that execution in the make test-merge-rules target.