[WebAssembly] Add new explicit relocation types for PIC relocations

See https://github.com/WebAssembly/tool-conventions/pull/106

Differential Revision: https://reviews.llvm.org/D59907

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357710 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed