[llvm] Modify llvm-gsymutil to ignore invalid file indexes (PR #71431)

[David Blaikie via llvm-commits]

dwblaikie wrote:

> line table contains entries with an invalid file index (line entry will be removed) inline functions that have invalid DW_AT_call_file file indexes when there are no line table entries for a function and we fall back to making a single line table entry from the functions DW_AT_decl_file/DW_AT_decl_line attributes, we make sure the DW_AT_decl_file attribute is valid before emitting it.

This is hard to follow - I guess it's mean to be a bulleted list of the different cases/how they're handled, but ends up as a big run-on sentence?

https://github.com/llvm/llvm-project/pull/71431