[llvm] [Dexter] Associate parser errors with correct file (PR #66765)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Manually pushed rather than merged in order to properly tag Ben Mudd as the commit author, which doesn't seem possible with Github merges, not counting an "Authored by" at the end of the commit message.

https://github.com/llvm/llvm-project/pull/66765