[WebAssembly] made assembler parse block_type

Summary:
This was previously ignored and an incorrect value generated.

Also fixed Disassembler's handling of block_type.

Reviewers: dschuff, aheejin

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D56092

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350270 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed