[llvm] [Profile] Use upper 32 bits of profile version for profile variants. (PR #67695)

[Petr Hosek via llvm-commits]

petrhosek wrote:

We could also consider just using 16 bits for flags rather than going all the way to 32, but I don't have a strong preference, either way is fine with me.

https://github.com/llvm/llvm-project/pull/67695