[BOLT][NFC] Use std::optional in RewriteInstance

[Amir]

e8d6c537ac7c1caea865860fd32c1ba2623c4ddc

bolt/include/bolt/Core/BinaryContext.h

public:
 
   /// Old .text info.
   uint64_t OldTextSectionAddress{0};
   uint64_t OldTextSectionOffset{0};
   uint64_t OldTextSectionSize{0};
 
   /// Address of the code/function that is executed before any other code in
   /// the binary.
-  Optional<uint64_t> StartFunctionAddress;
+  std::optional<uint64_t> StartFunctionAddress;
 
   /// Address of the code/function that is going to be executed right before
   /// the execution of the binary is completed.
-  Optional<uint64_t> FiniFunctionAddress;
+  std::optional<uint64_t> FiniFunctionAddress;
 
   /// Page alignment used for code layout.
   uint64_t PageAlign{HugePageSize};
 
   /// True if the binary requires immediate relocation processing.
   bool RequiresZNow{false};
 
   /// List of functions that always trap.

bolt/lib/Rewrite/MachORewriteInstance.cpp

std::vector<DataInCodeRegion> readDataInCode(const MachOObjectFile &O) {
   for (auto I = O.begin_dices(), E = O.end_dices(); I != E; ++I)
     DataInCode.emplace_back(*I);
   llvm::stable_sort(DataInCode, [](DataInCodeRegion LHS, DataInCodeRegion RHS) {
     return LHS.Offset < RHS.Offset;
   });
   return DataInCode;
 }
 
-Optional<uint64_t> readStartAddress(const MachOObjectFile &O) {
-  Optional<uint64_t> StartOffset;
-  Optional<uint64_t> TextVMAddr;
+std::optional<uint64_t> readStartAddress(const MachOObjectFile &O) {
+  std::optional<uint64_t> StartOffset;
+  std::optional<uint64_t> TextVMAddr;
   for (const object::MachOObjectFile::LoadCommandInfo &LC : O.load_commands()) {
     switch (LC.C.cmd) {
     case MachO::LC_MAIN: {
       MachO::entry_point_command LCMain = O.getEntryPointCommand(LC);
       StartOffset = LCMain.entryoff;
       break;
     }
     case MachO::LC_SEGMENT: {
case MachO::LC_SEGMENT_64: {
         TextVMAddr = LCSeg.vmaddr;
       break;
     }
     default:
       continue;
     }
   }
   return (TextVMAddr && StartOffset)
-             ? Optional<uint64_t>(*TextVMAddr + *StartOffset)
+             ? std::optional<uint64_t>(*TextVMAddr + *StartOffset)
              : std::nullopt;
 }
 
 } // anonymous namespace
 
 void MachORewriteInstance::discoverFileObjects() {
   std::vector<SymbolRef> FunctionSymbols;
   for (const SymbolRef &S : InputFile->symbols()) {

bolt/lib/Rewrite/RewriteInstance.cpp

if (Function) {
       }
     }
 
     // Handle special symbols based on their name.
     Expected<StringRef> SymbolName = Symbol.getName(StringSection);
     assert(SymbolName && "cannot get symbol name");
 
     auto updateSymbolValue = [&](const StringRef Name,
-                                 Optional<uint64_t> Value = std::nullopt) {
+                                 std::optional<uint64_t> Value = std::nullopt) {
       NewSymbol.st_value = Value ? *Value : getNewValueForSymbol(Name);
       NewSymbol.st_shndx = ELF::SHN_ABS;
       outs() << "BOLT-INFO: setting " << Name << " to 0x"
              << Twine::utohexstr(NewSymbol.st_value) << '\n';
     };
 
     if (opts::HotText &&
         (*SymbolName == "__hot_start" || *SymbolName == "__hot_end")) {