[lld] [lld][ELF] Add --debug-names to create merged .debug_names. (PR #86508)

[Greg Clayton via llvm-commits]

clayborg wrote:

I like the idea of having a single .debug_names section and don't want to get in the way of that. My PR for addng support for foreign type units hasn't gone in yet either, so I am happy to change course here. We just need a way to be able ensure that .debug_names entries for foreign type units somehow know if they are valid or not. Our previous attempt at this was to add a DW_AT_dwo_name attribute to the DW_TAG_type_unit and then verify that this matched the one any only CU in the CU list of the .debug_names table, but happy to pivot if we can think of a better way to do this. @dwblaikie any ideas?

https://github.com/llvm/llvm-project/pull/86508