[lldb] Fix dangling expression

This fixes the following:
```
[6603/7618] Building CXX object
tools\lldb\source\Plugins\ObjectFile\PECOFF\CMakeFiles\lldbPluginObjectFilePECOFF.dir\WindowsMiniDump.cpp.obj
C:\src\git\llvm-project\lldb\source\Plugins\ObjectFile\PECOFF\WindowsMiniDump.cpp(29,25):
warning: object backing the pointer will be destroyed at the end of the
full-expression [-Wdangling-gsl]
   29 |   const auto &outfile = core_options.GetOutputFile().value();
         |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
	 1 warning generated.
```

Author: aganea

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

@@ -26,7 +26,8 @@ bool SaveMiniDump(const lldb::ProcessSP &process_sp,
   if (!process_sp)
     return false;
 #ifdef _WIN32
-  const auto &outfile = core_options.GetOutputFile().value();
+  std::optional<FileSpec> outfileSpec = core_options.GetOutputFile();
+  const auto &outfile = outfileSpec.value();
   HANDLE process_handle = ::OpenProcess(
       PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, FALSE, process_sp->GetID());
   const std::string file_name = outfile.GetPath();