[WebAssembly] Allow each data segment to specify its own alignment

Also, add a flags field as we will almost certainly
be needing that soon too.

Differential Revision: https://reviews.llvm.org/D38296

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314534 91177308-0d34-0410-b5e6-96231b3b80d8
19 files changed