[llvm] [BPF] Support Jump Table (PR #149715)

[Anton Protopopov via llvm-commits]

aspsk wrote:

@yonghong-song A side note. I am constantly getting 
```
In file included from /home/aspsk/src/llvm-project/llvm/lib/Target/BPF/BPFISelLowering.h:17,
                 from /home/aspsk/src/llvm-project/llvm/lib/Target/BPF/BPFSubtarget.h:17,
                 from /home/aspsk/src/llvm-project/llvm/lib/Target/BPF/BPFSubtarget.cpp:13:
/home/aspsk/src/llvm-project/llvm/lib/Target/BPF/BPF.h:25:20: warning: ‘llvm::BPF_TRAP’ defined but not used [-Wunused-variable]
   25 | static const char *BPF_TRAP = "__bpf_trap";
      |                    ^~~~~~~~
```
Is this a not removed leftover from an old version?

https://github.com/llvm/llvm-project/pull/149715