Prior to funcref, a partial chunk of an invalid module was never needed,
but funcref allows a partially instantiated module to modify imported
tables with references to its own functions, which means we need to keep
the second module alive while that function reference is present within
the imported table.
This was tested by the spectests, but very rarely caught as our GC does
not behave particularly predictably, making it so the offending module
remains in memory just long enough to let the tests pass.
This commit makes it so all function references keep their respective
modules alive.
a60ecea16a