[WebAssembly] Handle _setjmp and _longjmp in SjLj

In some platforms `_setjmp` and `_longjmp` are used instead of `setjmp`
and `longjmp`. This CL adds support for them.

Fixes https://github.com/emscripten-core/emscripten/issues/14999.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D109669