[llvm] [RemoveDIs][DebugInfo][IR] Add parsing for non-intrinsic debug values (PR #79818)

[Jeremy Morse via llvm-commits]

jmorse wrote:

For the mixing-old-and-new issue, AFAIUI the population of people hand-writing debug-info IR tests is small, and we usually copy existing tests to write them. It's also not a syntactic problem to report as parsing will succeed, but the Module will be ill formed, it's more akin to a Verifier error but it makes the most sense to detect it in the parser (to avoid answering questions about what mixture of old/new debug-info should be permitted).

IMO: it'd be better to print out an informative error at the end of parsing, something like "#dbg_* records were encountered during parsing, but llvm.dbg.* intrinsics were seen in functions [list first ten users of the relevant declaration?]. Cannot load a module with both flavours of debug-info". That avoids the invasive code changes but gives a good diagnosis of what's gone wrong.

https://github.com/llvm/llvm-project/pull/79818