[llvm] [DebugInfo] DWARF Units without DIEs are okay (PR #88840)

[Will Hawkins via llvm-commits]

hawkinsw wrote:

As I have said before, @clayborg and others, I have really enjoyed working with the DebugInfo library! I am working on a patch to GDB to add support for `DW_LNCT_LLVM_source` (you can see the 5th revision here: https://sourceware.org/pipermail/gdb-patches/2024-April/208063.html). 

While working on that issue, I noticed that `llvm-dwarfdump` (an *amazing* tool) was throwing out spurious warnings for CUs that do not have DIEs. There does not seem to be anything in the standard that says that such a situation cannot occur. 

I have worked up the little PR that I just submitted to make things "happier". I am _sure_ that there is something that I did wrong. If you think that this is something that you would accept and there are things that I can change to make it better, please let me know!

Thanks for making DebugInfo so awesome.

https://github.com/llvm/llvm-project/pull/88840