[clang] [clang][x86][bytecode] Replace interp__builtin_parity/clrsb/bitreverse/ffs with static bool interp__builtin_elementwise_int_unaryop callback (PR #162346)

[via cfe-commits]

================
@@ -3209,7 +3182,11 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
   case Builtin::BI__builtin_ffs:
   case Builtin::BI__builtin_ffsl:
   case Builtin::BI__builtin_ffsll:
-    return interp__builtin_ffs(S, OpPC, Frame, Call);
+    return interp__builtin_elementwise_int_unaryop(
+        S, OpPC, Call, [](const APSInt &Val) {
----------------
donneypr wrote:

Just my novice 2 cents: If we're keeping the trailing return type for some of the functions eg. `Val.reverseBits()`, I think it would better to add it to all of them for uniformity. 

https://github.com/llvm/llvm-project/pull/162346