[WebAssembly] Add asm.js-style setjmp/longjmp handling for wasm (reland r280302)

Summary: This patch adds asm.js-style setjmp/longjmp handling support for WebAssembly. It also uses JavaScript's try and catch mechanism.

Reviewers: jpp, dschuff

Subscribers: jfb, dschuff

Differential Revision: https://reviews.llvm.org/D24121

llvm-svn: 280415