[cmake] should put output in build dir

CMakeLists.txt

@@ -26,7 +26,7 @@ endif ()
 
 # put output in "bin"
 
-set(OUTPUT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/bin)
+set(OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/bin)
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${OUTPUT_DIR})
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${OUTPUT_DIR})
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${OUTPUT_DIR})