[WebAssembly] MC: Create wasm data segments based on MCSections

This means that we can honor -fdata-sections rather than
always creating a segment for each symbol.

It also allows for a followup change to add .init_array and friends.

Differential Revision: https://reviews.llvm.org/D37876

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313395 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed