/usr/include/php/20151012/ext/ is in php-apcu 5.1.3+4.0.10-1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/php/20151012/ext/apcu/
/usr/include/php/20151012/ext/apcu/apc.h
/usr/include/php/20151012/ext/apcu/apc_api.h
/usr/include/php/20151012/ext/apcu/apc_arginfo.h
/usr/include/php/20151012/ext/apcu/apc_cache.h
/usr/include/php/20151012/ext/apcu/apc_cache_api.h
/usr/include/php/20151012/ext/apcu/apc_globals.h
/usr/include/php/20151012/ext/apcu/apc_iterator.h
/usr/include/php/20151012/ext/apcu/apc_lock.h
/usr/include/php/20151012/ext/apcu/apc_lock_api.h
/usr/include/php/20151012/ext/apcu/apc_pool.h
/usr/include/php/20151012/ext/apcu/apc_pool_api.h
/usr/include/php/20151012/ext/apcu/apc_serializer.h
/usr/include/php/20151012/ext/apcu/apc_sma.h
/usr/include/php/20151012/ext/apcu/apc_sma_api.h
/usr/include/php/20151012/ext/apcu/apc_stack.h
/usr/include/php/20151012/ext/apcu/php_apc.h