[llvm] [NFC][LV] Introduce enums for uncountable exit detail and style (PR #184808)

[Graham Hunter via llvm-commits]

================
@@ -905,16 +905,14 @@ void VPlanTransforms::createInLoopReductionRecipes(
     R->eraseFromParent();
 }
 
-void VPlanTransforms::handleEarlyExits(VPlan &Plan,
-                                       bool HasUncountableEarlyExit) {
+void VPlanTransforms::handleEarlyExits(VPlan &Plan, EarlyExitStyle Style) {
----------------
huntergr-arm wrote:

So there was a request on the transform PR (https://github.com/llvm/llvm-project/pull/178454#discussion_r2853946178) to not pull LoopVectorizationLegality.h in to VPlanTransforms.h, which means I can't pass the details enum to that transform (well, I guess I could use an `unsigned` in the header and cast it in the .cpp file, but that's a bit ugly).

I don't think there's a good shared header for it, so I'm instead mapping one to the other in LoopVectorize.cpp. As the comment there notes, it's just 1-1 right now, but we may have other styles to use later.

https://github.com/llvm/llvm-project/pull/184808