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

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> Let me know if this has been discussed elsewhere, but why is necessary to add a new `#` token to the grammar?

The purpose of the leading `#` is to create a syntactic distinction from instructions. Without using a leading symbol to specify that a non-instruction line is beginning, the only discriminating feature would be whitespace - which is not clear enough by itself, and can't be used by the parser.
The reason why `#` specifically is used here is simply that it's free real estate - most other symbols that LLVM uses followed by letters are already classified as specific tokens (i.e. `!foo`, `@foo`, `$foo`, etc) that we'd ideally avoid overloading if alternatives are available.

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