[WebAssembly] Stop generating helper functions in WebAssemblyLowerEmscriptenEHSjLj
Previously we were creating weakly defined helper function in
each translation unit:
Instead we now assume these will be provided at link time. In
emscripten they are provided in compiler-rt:
Additionally we previously created three global variable which are
also now required to exist at link time instead.
Differential Revision: https://reviews.llvm.org/D49208