Platform: include version-specific APIs in Doxygen, too.

src/Magnum/Platform/GlfwApplication.h

@@ -276,7 +276,7 @@ class GlfwApplication::Configuration {
          * @see @ref Flags, @ref setFlags(), @ref Context::Flag
          */
         enum class Flag: Int {
-            #ifdef GLFW_CONTEXT_NO_ERROR
+            #if defined(DOXYGEN_GENERATING_OUTPUT) || defined(GLFW_CONTEXT_NO_ERROR)
             /**
              * Specifies whether errors should be generated by the context.
              * If enabled, situations that would have generated errors instead
@@ -308,7 +308,7 @@ class GlfwApplication::Configuration {
             Resizeable = 1 << 1,   /**< Resizeable window */
             Hidden = 1 << 2,       /**< Hidden window */
 
-            #ifdef GLFW_MAXIMIZED
+            #if defined(DOXYGEN_GENERATING_OUTPUT) || defined(GLFW_MAXIMIZED)
             /**
              * Maximized window
              *