[WebAssembly] Allow Wasm EH with Emscripten SjLj

We explicitly made it error out in D101403, out of a good intention that
the error message will make people less confusing. Turns out, we weren't
failing all cases of wasm EH + SjLj; only a few cases were failing and
our client was able to get around by fixing source code, but now we made
it fail for all cases, even the cases that previously succeeded fail,
which we didn't intend. This reverts that change.

Reviewed By: tlively

Differential Revision: https://reviews.llvm.org/D102364