Fix MSVC NUMA compile issues

closes https://github.com/official-stockfish/Stockfish/pull/5298

No functional change

src/misc.h

@@ -77,6 +77,8 @@ using AlignedPtr = std::unique_ptr<T, AlignedDeleter<T>>;
 template<typename T>
 using LargePagePtr = std::unique_ptr<T, LargePageDeleter<T>>;
 
+#if defined(__linux__)
+
 struct PipeDeleter {
     void operator()(FILE* file) const {
         if (file != nullptr)
@@ -86,8 +88,6 @@ struct PipeDeleter {
     }
 };
 
-#if defined(__linux__)
-
 inline std::optional<std::string> get_system_command_output(const std::string& command) {
     std::unique_ptr<FILE, PipeDeleter> pipe(popen(command.c_str(), "r"));
     if (!pipe)