Remove unused IsRetSigned field (#2567)

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@4add3896f5889e5

Author: svenvh

llvm-spirv/lib/SPIRV/OCLToSPIRV.cpp

@@ -943,7 +943,7 @@ void OCLToSPIRVBase::transBuiltin(CallInst *CI, OCLBuiltinTransInfo &Info) {
     Mutator.changeReturnType(
         Info.RetTy, [OldRetTy, &Info](IRBuilder<> &Builder, CallInst *NewCI) {
           if (Info.RetTy->isIntegerTy() && OldRetTy->isIntegerTy()) {
-            return Builder.CreateIntCast(NewCI, OldRetTy, Info.IsRetSigned);
+            return Builder.CreateIntCast(NewCI, OldRetTy, false);
           }
           return Builder.CreatePointerBitCastOrAddrSpaceCast(NewCI, OldRetTy);
         });

llvm-spirv/lib/SPIRV/OCLUtil.h

@@ -162,9 +162,7 @@ struct OCLBuiltinTransInfo {
   /// Postprocessor of operands
   std::function<void(BuiltinCallMutator &)> PostProc;
   Type *RetTy;      // Return type of the translated function
-  bool IsRetSigned; // When RetTy is int, determines if extensions
-                    // on it should be a sext or zet.
-  OCLBuiltinTransInfo() : RetTy(nullptr), IsRetSigned(false) {
+  OCLBuiltinTransInfo() : RetTy(nullptr) {
     PostProc = [](BuiltinCallMutator &) {};
   }
 };