Compilation fails on centos 7 with recent devtoolset

/usr/include/c++/4.8.2/atomic: In instantiation of 'struct std::atomic<std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long int, std::ratio<1l, 1000000000l> > > >': /project/open-vds/src/OpenVDS/VDS/VolumeDataPageAccessorImpl.h:50:67: required from here /usr/include/c++/4.8.2/atomic:167:7: error: function 'std::atomic<_Tp>::atomic() [with _Tp = std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long int, std::ratio<1l, 1000000000l> > >]' defaulted on its first declaration with an exception-specification that differs from the implicit declaration 'constexpr std::atomic<std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long int, std::ratio<1l, 1000000000l> > > >::atomic()' atomic() noexcept = default; ^

I don't think we need to use atomic for the m_lastUsed timestamp -- either that or we can just convert it to a plain int64_t which has milliseconds after startup (using the steady_clock).