[Client] Use __WINDOWS define

apps/openmw/mwmp/Networking.cpp

@@ -375,7 +375,7 @@ void Networking::preInit(std::vector<std::string> &content, Files::Collections &
 
     if (!checksumsResponse.empty()) // something wrong
     {
-#if defined(_MSC_VER)
+#if defined(__WINDOWS)
         errmsg = comparePlugins(checksums, checksumsResponse);
 #else
         errmsg = comparePluginsMonospaced(checksums, checksumsResponse);
@@ -386,7 +386,7 @@ void Networking::preInit(std::vector<std::string> &content, Files::Collections &
     {
         LOG_MESSAGE_SIMPLE(Log::LOG_ERROR, comparePluginsMonospaced(checksums, checksumsResponse, true).c_str());
         SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "tes3mp", errmsg.c_str(), 0);
-#if defined(_MSC_VER)
+#if defined(__WINDOWS)
         throw std::runtime_error("Shutting down.");
 #endif
         MWBase::Environment::get().getStateManager()->requestQuit();