[clang] [llvm] [HLSL] implement `clamp` intrinsic (PR #85424)

[Farzon Lotfi via cfe-commits]

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@@ -132,12 +134,60 @@ static bool expandRcpIntrinsic(CallInst *Orig) {
   return true;
 }
 
+static Intrinsic::ID getCorrectMaxIntrinsic(Type *elemTy,
+                                            Intrinsic::ID clampIntrinsic) {
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farzonl wrote:

Will do.

As an aside this function started off generic until I found out I couldn't use `getSignBit()` to distinguish unsigned clamp vs signed clamp. The only way I could determine signed-ness was in codeGen. 

https://github.com/llvm/llvm-project/pull/85424