Added CMake variables to select the modules to be built

This addresses issue #798.

src/SFML/CMakeLists.txt

@@ -49,11 +49,31 @@ set(CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake/Modules/")
 set(LIBRARY_OUTPUT_PATH "${PROJECT_BINARY_DIR}/lib")
 
 # add the modules subdirectories
+
+# sfml-system
 add_subdirectory(System)
+
+# sfml-main and sfml-activity
 if(SFML_OS_WINDOWS OR SFML_OS_ANDROID OR SFML_OS_IOS)
     add_subdirectory(Main)
 endif()
-add_subdirectory(Window)
-add_subdirectory(Network)
-add_subdirectory(Graphics)
-add_subdirectory(Audio)
+
+# sfml-window
+if(SFML_BUILD_WINDOW OR SFML_BUILD_GRAPHICS)
+    add_subdirectory(Window)
+endif()
+
+# sfml-network
+if(SFML_BUILD_NETWORK)
+    add_subdirectory(Network)
+endif()
+
+# sfml-graphics
+if(SFML_BUILD_GRAPHICS)
+    add_subdirectory(Graphics)
+endif()
+
+# sfml-audio
+if(SFML_BUILD_AUDIO)
+    add_subdirectory(Audio)
+endif()