[clang] [llvm] [clang][Modules][Serialization] Avoid serializing duplicate source location entries for shared input files (PR #209795)

[Ayokunle Amodu via cfe-commits]

ayokunle321 wrote:

> Did look up in the bug tracker which issues would be addressed by this change?

Just added them to the top of the PR description.

https://github.com/llvm/llvm-project/pull/209795