Support for eqref an other features of the GC MVP

[Horcrux7]

What is the status of the GC features? With version 1.0.17 I try:

(module
  (func $test(local $val eqref)
  )
)

I receive error: unexpected token "eqref", expected i32, i64, f32, f64, v128 or externref.

[binji]

I haven't gotten around to implementing those features yet. I've been wanting to make more progress, but have been pretty busy with other things.

[sbc100]

Closing as duplicate of #1257