[llvm] [TableGen] Split large printInstruction() for NVPTX to avoid compiler limits (PR #218530)

[Kazu Hirata via llvm-commits]

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kazutakahirata wrote:

Start `TotalSize` at `1` and drop the `NDEBUG` return guard. Unlike `assert()`, `llvm_unreachable()` expands to `LLVM_BUILTIN_UNREACHABLE` (`__builtin_unreachable()` / `__assume(false)`) in `NDEBUG` builds rather than a no-op, so control never falls through `case 0:`:
```suggestion
  std::vector<unsigned> OpcodeToOffset(NumberedInsts.size(), 0);
  unsigned TotalSize = 1;
```

https://github.com/llvm/llvm-project/pull/218530