[llvm] [NVPTX] Do not emit `.target debug` if only line tables are requested (PR #140146)

[Sergei Lebedev via llvm-commits]

superbobry wrote:

PTX ISA is somewhat ambiguous in that section, but empirically ptxas does accept PTX with `.section` directives without `.target debug`.

https://github.com/llvm/llvm-project/pull/140146