[WebAssembly] Default to something reasonable in WebAssemblyAddMissingPrototypes
Previously if we couldn't derive a prototype for a "no-prototype"
function from C we would leave it as is:
void foo(...)
With this change we instead give is an empty signature and remove
the "no-prototype" attribute.
This fixes the current wasm waterfall test failure.
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D58488
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354544 91177308-0d34-0410-b5e6-96231b3b80d8