[WebAssembly] Prevent inline assembly from being mangled by SjLj

Summary:
Before, inline assembly gets mangled by the SjLj transformation.

For example, in a function with setjmp/longjmp, this LLVM IR code

    call void asm sideeffect "", ""()

would be transformed into

    call void @__invoke_void(void ()* asm sideeffect "", "")

This is invalid, and results in the error:

    Cannot take the address of an inline asm!

In this diff, we skip the transformation for inline assembly.

Reviewers: aheejin, tlively

Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64115

llvm-svn: 364985