- fixed cross-compilation support

Lemon's post build command aborts configuration step after CMake version bump to 3.1.0 in ba618d3
When CMake version was 2.8.7 the same command produced a warning

CMake Error at tools/lemon/CMakeLists.txt:11 (add_custom_command):
  TARGET 'lemon' is IMPORTED and does not build here.

tools/lemon/CMakeLists.txt

@@ -5,10 +5,10 @@ if( NOT CMAKE_CROSSCOMPILING )
 
 	add_executable( lemon lemon.c )
 	set( CROSS_EXPORTS ${CROSS_EXPORTS} lemon PARENT_SCOPE )
-endif()
 
-# Lemon wants lempar.c in its directory
-add_custom_command( TARGET lemon
-	POST_BUILD
-	COMMAND echo $<TARGET_FILE_DIR:lemon>
-	COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_SOURCE_DIR}/lempar.c $<TARGET_FILE_DIR:lemon> )	
+	# Lemon wants lempar.c in its directory
+	add_custom_command( TARGET lemon
+		POST_BUILD
+		COMMAND echo $<TARGET_FILE_DIR:lemon>
+		COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_SOURCE_DIR}/lempar.c $<TARGET_FILE_DIR:lemon> )	
+endif()