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

[David Blaikie via llvm-commits]

dwblaikie wrote:

> DWARF produced by LTO and BOLT can sometimes be broken where file indexes are beyond the end of the line table's file list in the prologue. 

Bugs are always possible, but I'm pretty sure LTO would haev a hard time producing this sort of bug... - maybe BOLT's the root cause? In any case, as noted previously, some kind of bug reports would be appreciated.

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