Update build.sh (micro-ROS#360) (micro-ROS#362)

(cherry picked from commit 53c60de)

Co-authored-by: Pablo Garrido <[email protected]>

Author: mergify[bot]

config/generate_lib/generic/build.sh

@@ -46,7 +46,7 @@ pushd $FW_TARGETDIR/mcu_ws >/dev/null
 		done; \
 		cd ..; rm -rf $folder; \
 	done ; \
-	ar rc libmicroros.a $(ls *.o *.obj); mkdir -p $BUILD_DIR; cp libmicroros.a $BUILD_DIR; ranlib $BUILD_DIR/libmicroros.a; \
+	ar rc libmicroros.a $(ls *.o *.obj 2> /dev/null); mkdir -p $BUILD_DIR; cp libmicroros.a $BUILD_DIR; ranlib $BUILD_DIR/libmicroros.a; \
     cp -R $FW_TARGETDIR/mcu_ws/install/include $BUILD_DIR/; \
 	cd ..; rm -rf libmicroros;