std::strlen requires cstring include to build

Or, even simpler, don't bother with the needless namespacing.

Change-Id: I4bbb115c1c2c89881a0bf88ccd54b0f5cb8b3518
(cherry picked from commit da9bd301c6f62e829daadb2af6a6b9633d4f1cb9)
Signed-off-by: Andras Timar <andras.timar@collabora.com>