disable cocoa opengl on cmake

CMakeLists.txt

@@ -60,11 +60,8 @@ endif()
 
 if(MW_TRY_OPENGL)
   find_package(OpenGL)
-  if(OpenGL_FOUND)
+  if(OpenGL_FOUND and NOT APPLE)
     set(MW_BUILD_OPENGL ON)
-    if(APPLE)
-      list(APPEND SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/src/widget/opengl_cocoa.m")
-    endif()
     message(STATUS "OpenGL widget has been enabled")
   else()
     message(WARNING "OpenGL widget has been disabled")

src/backend/nococoa.m

@@ -1,4 +1,5 @@
 #include <Mw/Milsko.h>
+#import <AppKit/AppKit.h>
 
 void MwLLNoCocoaErrorMessage(void) {
 	NSAlert* alert = [[NSAlert alloc] init];