[SYCL][NFC] Use std::nullopt instead of llvm::None (#7926)

llvm::None is deprecated and causes warnings and can cause build fails
in the future.

Author: Fznamznon

clang/lib/AST/Expr.cpp

@@ -646,7 +646,7 @@ UniqueStableNameDiscriminator(ASTContext &, const NamedDecl *ND) {
   if (const auto *RD = dyn_cast<CXXRecordDecl>(ND))
     if (RD->isLambda())
       return RD->getDeviceLambdaManglingNumber();
-  return llvm::None;
+  return std::nullopt;
 }
 
 std::string SYCLUniqueStableNameExpr::ComputeName(ASTContext &Context,

clang/tools/clang-offload-wrapper/ClangOffloadWrapper.cpp

@@ -1374,7 +1374,7 @@ class BinaryWrapper {
     bool ExecutionFailed = false;
     std::string ErrMsg;
     (void)sys::ExecuteAndWait(ObjcopyPath, Args,
-                              /*Env=*/llvm::None, /*Redirects=*/{},
+                              /*Env=*/std::nullopt, /*Redirects=*/{},
                               /*SecondsToWait=*/0,
                               /*MemoryLimit=*/0, &ErrMsg, &ExecutionFailed);