[llvm] CodeGen: Derive ARM EH pointer/selector registers from MCAsmInfo (PR #226109)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> SJLJ exception handling is almost entirely a library feature, not an object file or architecture feature. It just requires that the target implements the setjmp() intrinsic. Basically, entering a "try" is lowered to setjmp(), and throwing an exception is lowered to longjmp(). The primary upside is that the implementation requires almost no platform-specific code, so it's very easy to port to new platforms.

So in that case, is the meaning of `getExceptionPointerRegister` approximately which register is used as the argument to setjmp, which could be arbitrary code? In that case this patch is probably the wrong way to go 

https://github.com/llvm/llvm-project/pull/226109