cmake: replace 'stub' with 'no-op/no_op'

this might be slightly more aligned with the intent.
previously:
5205bfe79e cmake: replace 'dummy' with 'stub'

Change-Id: Id2528b157613bbe2c61e060cba0843ecd363c435
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3b45e21..dcaf7ce 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -219,7 +219,7 @@
 
 # Targets
 add_library(aom_version ${AOM_VERSION_SOURCES})
-add_stub_source_file_to_target(aom_version c)
+add_no_op_source_file_to_target(aom_version c)
 add_custom_command(OUTPUT "${AOM_CONFIG_DIR}/config/aom_version.h"
                    COMMAND ${CMAKE_COMMAND} ARGS
                            -DAOM_CONFIG_DIR=${AOM_CONFIG_DIR}
@@ -781,7 +781,7 @@
     # here, it really is the Xcode generator's fault, or just a deficiency in
     # Xcode itself.
     foreach(aom_app ${AOM_APP_TARGETS})
-      add_stub_source_file_to_target("${aom_app}" "cc")
+      add_no_op_source_file_to_target("${aom_app}" "cc")
     endforeach()
   endif()
 endif()