Avoid warnings on cast from char* to QString

Why isn't QtQml being built with those functions disabled, so they
produce errors?

Change-Id: I2c0cf945523142800982f100a61a6c10e1929632
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>