[llvm] [CMake][Windows] Fix Debug config build when using MSBuild (PR #111765)

[NAKAMURA Takumi via llvm-commits]

https://github.com/chapuni requested changes to this pull request.

I've reconfirmed `LLVM_TABLEGEN` is `llvm-tblgen` by default.

- VS Buildtools
- CMake-3.30.5
- Regardless of `LLVM_OPTIMIZED_TABLEGEN`

Don't override `LLVM_TABLEGEN` without the reason. Use `LLVM_NATIVE_TOOLS_DIR` for the purpose.

https://github.com/llvm/llvm-project/pull/111765