[WebAssembly] Fix some broken type encodings in wasm binary

A recent change switch the in-memory wasm value types
to be signed integers, but I missing a few cases where
these were being writing to the binary.

Differential Revision: https://reviews.llvm.org/D31014

Patch by Sam Clegg

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297991 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed