[lldb] Add #include <optional> (NFC)

This patch adds #include <optional> to those files containing
llvm::Optional<...> or Optional<...>.

I'll post a separate patch to actually replace llvm::Optional with
std::optional.

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

lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp

@@ -38,6 +38,7 @@
 #include "llvm/Support/FormatAdapters.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include <optional>
 
 #define IMAGE_DOS_SIGNATURE 0x5A4D    // MZ
 #define IMAGE_NT_SIGNATURE 0x00004550 // PE00