[llvm] [IR] Add CallBr intrinsics support (PR #133907)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

Re the example:
```llvm
  callbr void @llvm.amdgcn.kill(i1 %c) to label %cont [label %kill]
kill:
  unreachable
cont:
  ...
```
the `to label` is supposed to be the "fallthrough case" where the instruction doesn't take a branch to anything in the indirect label list `[label <foo>]`.  Should the example instead be:
```llvm
  callbr void @llvm.amdgcn.kill(i1 %c) to label %cont [label %kill]
cont:
  ...
kill:
  unreachable
```
I guess are those the same? idk, example just looked funny.

https://github.com/llvm/llvm-project/pull/133907