[WebAssembly] Add support for dylink section in object format

See https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md.

Differential Revision: https://reviews.llvm.org/D54490

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346880 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed