[clang] [lld] [llvm] Reland "Compute GUIDs once and store in metadata" (#184065) (PR #201849)

[Shilei Tian via cfe-commits]

shiltian wrote:

IIUC, this doesn't work with `-mlink-builtin-bitcode-postopt` if the linked bitcode doesn't have GUIDs assigned to its global variables. Is that expected?

Do we now require `-mlink-builtin-bitcode-postopt` not to be used with LTO compilation? If so, would it make more sense to emit some kind of warning?

If `-mlink-builtin-bitcode-postopt` is expected to continue working, should we move the pass to a later point in the pipeline?

@mtrofin 

https://github.com/llvm/llvm-project/pull/201849