Make sure std::size_t is defined when it's being used

Change-Id: I40a3fbed0a32b8739f3c2c46a88e00efa12c228d
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>
Signed-off-by: Chet Kener <Cl3Kener@gmail.com>