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

[Anton Protopopov via llvm-commits]

aspsk wrote:

@yonghong-song (Sorry, need to stop testing today, will have ~2 hours tomorrow.) I've tried your branch, and my current patch fails because the JT symbols now have the `R_BPF_64_NODYLD32` relocation type. Is this expected?

```
Relocation section '.rel.jumptables' at offset 0xc60 contains 4 entries:
    Offset             Info             Type               Symbol's Value  Symbol's Name
0000000000000000  0000000200000004 R_BPF_64_NODYLD32      0000000000000000 syscall
0000000000000004  0000000200000004 R_BPF_64_NODYLD32      0000000000000000 syscall
0000000000000008  0000000200000004 R_BPF_64_NODYLD32      0000000000000000 syscall
000000000000000c  0000000200000004 R_BPF_64_NODYLD32      0000000000000000 syscall
```

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