cmake: fix the creation dummy main to avoid rebuilding

tools/cmake/idf_functions.cmake

@@ -188,7 +188,10 @@ function(idf_add_executable)
         # Create a dummy file to work around CMake requirement of having a source
         # file while adding an executable
         add_executable(${exe_target} "${CMAKE_CURRENT_BINARY_DIR}/dummy_main_src.c")
-        file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/dummy_main_src.c)
+        add_custom_command(OUTPUT dummy_main_src.c
+            COMMAND ${CMAKE_COMMAND} -E touch dummy_main_src.c
+            WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+            VERBATIM)
 
         add_custom_target(dummy_main_src DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/dummy_main_src.c)