Reland "[WebAssembly] Add visibility flag to Wasm symbol flags""

Original change was rL319488.

This was reverted rL319602 due to a gcc 7.1 warning.

Differential Revision: https://reviews.llvm.org/D40772

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319626 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed