[clang] [Clang][LTO] Assign GUIDs after post-opt bitcode linking (PR #211155)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 approved this pull request.

Seems fine, `-mlink-builtin-bitcode` is already a hack and this just adds to it.

https://github.com/llvm/llvm-project/pull/211155