[llvm] Use thinlto and pgo for x86_64 windows release packaging (PR #71067)

[Pierrick Bouvier via llvm-commits]

pbo-linaro wrote:

That would be a nice addition @zmodem.
I know it's a boring request, but could you evaluate separately benefits from PGO alone, and then adding ThinLTO?
Same applies if we add BOLT too.
Build times should be checked too ideally.

Regarding the external source file used for profiling (`pgo_training-1.ii`), I don't know LLVM policy, but maybe it would be better to host it on our side, so we're sure it does not disappear one of those days.

Finally, aarch64 build could benefit from that too, but that can be done later.

https://github.com/llvm/llvm-project/pull/71067