build failure: initializetask.cpp:62:8: error: ‘random_device’ is not a member of ‘std’

I've tried with
&nbsp; GCC `5.5.0` and `7.3.0`
and flags
&nbsp; `-std=c++11`
&nbsp; `-std=gnu++11`
&nbsp; `-std=c++0x`
&nbsp; `-std=gnu++0x`

but I always hit the same
> initializetask.cpp:62:8: error: ‘random_device’ is not a member of ‘std’

(current commit 626051d)

What am I missing?