[llvm] [VPlan] Use bitfield to store Cmp predicates and GEP wrap flags. (NFC) (PR #181571)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

we're seeing `Assertion failed: (OpType != OperationType::FCmp || FCmpFlags.CmpPredStorage == Other.FCmpFlags.CmpPredStorage) && "Cannot drop CmpPredicate", file C:\b\s\w\ir\cache\builder\src\third_party\llvm\llvm\lib\Transforms\Vectorize\VPlanRecipes.cpp, line 343` assertions after this, but only on windows hosts. seems like the bitfield stuff is getting miscompiled, or there's UB only manifesting in windows builds?

https://github.com/llvm/llvm-project/pull/181571