add option for reference-types

[Gentle]

only enables the wasmtime feature, which allows initializing Modules that were compiled with newer llvm versions but don't actually use reference-types

[Gentle]

I tried with my own code and could successfully initialize a Module that errors without the option.

Since there is nothing actually implemented, I set the default to false and keep the feature disabled for fuzzers, I hope that is correct

[fitzgen]

Can you extend the wasm_validate function to disallow the following reference-types instructions:

• ref.null
• ref.is_null
• the typed variant of select
• ref.func
• table.get
• table.set
• table.size
• table.grow
• table.fill
• table.init
• table.copy

?

And also please add the following tests:

• a table-modifying instruction is used when reference-types are enabled, but the wasm is still rejected
• reference-types are enabled and an instruction encoding that requires reference-types is used for an instruction which doesn't actually mutate tables or manipulate references, and therefore wizer succeeds (for example, a call_indirect using a non-zero table index)

Thanks!

[Gentle]

I hope I added everything

[fitzgen]

Thanks! Two minor things and then we can merge this.

[Gentle]

I hope I did it right, this seems to use the new call_indirect and the second table

[Gentle]

as expected the test now goes red if I disable reference-types, so it uses the right call now :)

Edit: actually that statement is not neccessarily true, with reference types disabled it already rejects the existence of a second table, but still, the fact that call_indirect finds the second table means it should be the new call_indirect

[fitzgen]

Thanks!