CSharp meta examples only re-compile when dependencies change.

Resolve issue #3557

examples/meta/csharp/CMakeLists.txt

@@ -14,11 +14,15 @@ FOREACH(META_EXAMPLE ${META_EXAMPLES})
 	get_filename_component(EXAMPLE_REL_DIR ${FULL_DIR} NAME)
 	set(EXAMPLE_NAME_WITH_DIR "${EXAMPLE_REL_DIR}-${EXAMPLE_NAME}")
 
-	ADD_CUSTOM_COMMAND(OUTPUT compiled_csharp_${EXAMPLE_NAME_WITH_DIR}
+	ADD_CUSTOM_COMMAND(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${EXAMPLE_REL_DIR}/${EXAMPLE_NAME}.exe
 		COMMAND	${CSHARP_COMPILER} ${EXAMPLE_NAME}.cs ${CSHARP_FLAGS} -out:${EXAMPLE_NAME}.exe
 		DEPENDS csharp_modular
 		WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/${EXAMPLE_REL_DIR})
-	LIST(APPEND CSHARP_EXAMPLES compiled_csharp_${EXAMPLE_NAME_WITH_DIR})
+
+	ADD_CUSTOM_TARGET(csharp_${EXAMPLE_NAME} ALL
+		DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${EXAMPLE_REL_DIR}/${EXAMPLE_NAME}.exe)
+
+	LIST(APPEND CSHARP_EXAMPLES csharp_${EXAMPLE_NAME})
 
 	add_test(NAME generated_csharp-${EXAMPLE_NAME_WITH_DIR}
 		WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/${EXAMPLE_REL_DIR}