Apply warning flags to RemoteVstPlugin too (#7389)

plugins/VstBase/CMakeLists.txt

@@ -33,6 +33,7 @@ set(export_variables
 		"LMMS_BUILD_WIN32"
 		"PLUGIN_DIR"
 		"LMMS_HAVE_LIBRT"
+		"USE_WERROR"
 )
 
 SET(EXTERNALPROJECT_CMAKE_ARGS

plugins/VstBase/RemoteVstPlugin.cpp

@@ -842,7 +842,6 @@ void RemoteVstPlugin::initEditor()
 #endif
 
 #else
-	XEvent e;
 	Atom prop_atom, val_atom;
 	
 	if (m_display == nullptr)
@@ -2301,7 +2300,7 @@ void RemoteVstPlugin::guiEventLoop()
 		{
 			XNextEvent(m_display, &e);
 		
-			if (e.type == ClientMessage && e.xclient.data.l[0] == m_wmDeleteMessage)
+			if (e.type == ClientMessage && static_cast<Atom>(e.xclient.data.l[0]) == m_wmDeleteMessage)
 			{
 				hideEditor();
 			}

plugins/VstBase/RemoteVstPlugin/CMakeLists.txt

@@ -1,4 +1,9 @@
-cmake_minimum_required(VERSION 3.8)
+cmake_minimum_required(VERSION 3.13)
+
+if(POLICY "CMP0092")
+	cmake_policy(SET CMP0092 NEW) # MSVC warning flags are not in CMAKE_<LANG>_FLAGS by default.
+endif()
+
 project(RemoteVstPlugin 
 	LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 17)
@@ -22,6 +27,9 @@ FOREACH( OUTPUTCONFIG ${CMAKE_CONFIGURATION_TYPES} )
 	SET("CMAKE_RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG}" "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}")
 ENDFOREACH()
 
+# Add warning and error flags
+include(ErrorFlags)
+
 # Import of windows.h breaks min()/max()
 add_definitions(-DNOMINMAX)