[InterfaceStub] Use std::optional in ELFObjHandler.cpp (NFC)

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

llvm/lib/InterfaceStub/ELFObjHandler.cpp

@@ -17,6 +17,7 @@
 #include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include <optional>
 
 using llvm::object::ELFObjectFile;
 
@@ -31,13 +32,13 @@ namespace ifs {
 struct DynamicEntries {
   uint64_t StrTabAddr = 0;
   uint64_t StrSize = 0;
-  Optional<uint64_t> SONameOffset;
+  std::optional<uint64_t> SONameOffset;
   std::vector<uint64_t> NeededLibNames;
   // Symbol table:
   uint64_t DynSymAddr = 0;
   // Hash tables:
-  Optional<uint64_t> ElfHash;
-  Optional<uint64_t> GnuHash;
+  std::optional<uint64_t> ElfHash;
+  std::optional<uint64_t> GnuHash;
 };
 
 /// This initializes an ELF file header with information specific to a binary