[WebAssembly] Explicitly specify function/global index space in YAML

These indexes are useful because they are not always zero based and
functions and globals are referenced elsewhere by their index.

This matches what we already do for the type index space.

Differential Revision: https://reviews.llvm.org/D41877

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322121 91177308-0d34-0410-b5e6-96231b3b80d8
23 files changed