Build: Set object extension to .o in NS toolchain

Change-Id: Ia19b8272d6bab59f038f78ebe5d91f93e46af24b
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/platform/ns/toolchain_ns_ARMCLANG.cmake b/platform/ns/toolchain_ns_ARMCLANG.cmake
index ea1c88a..66af662 100644
--- a/platform/ns/toolchain_ns_ARMCLANG.cmake
+++ b/platform/ns/toolchain_ns_ARMCLANG.cmake
@@ -23,7 +23,7 @@
 # at a particular step in the compiler initialisation. It is used here to
 # configure the extensions for object files. Despite the name, it also works
 # with the Ninja generator.
-#set(CMAKE_USER_MAKE_RULES_OVERRIDE ${CMAKE_CURRENT_LIST_DIR}/cmake/set_extensions.cmake)
+set(CMAKE_USER_MAKE_RULES_OVERRIDE ${CMAKE_CURRENT_LIST_DIR}/set_extensions.cmake)
 
 if(NOT DEFINED CMAKE_OBJCOPY)
     set(CMAKE_OBJCOPY ${CROSS_COMPILE}-objcopy CACHE FILEPATH "Path to objcopy")