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

[Pierrick Bouvier via llvm-commits]

pbo-linaro wrote:

Thanks for taking the time to check the different configurations.

Using LLVM source code for profiling data is a good solution IMHO.
For any reasonable complicated project using "most" of C++ features, it should bring similar data.

The price for ThinLTO is surprisingly high (in memory usage too I guess), and compared to PGO alone, the added value is pretty low in this case. Considering the numbers, I agree with you to only do PGO, as it's almost "free".

If we go with the PGO only version, it could be nice to directly factorize this for all architecture ([`do_build_libxml`](https://github.com/llvm/llvm-project/blob/ba13978f4269f4f35f7d1c32bb529f19bf1d8f46/llvm/utils/release/build_llvm_release.bat#L370) function provides an example).


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