Persistent warning with g++-8.x

[Paul Hargrove]

g++-8.2 produces the following warning, and others very similar, in many upcxx test compilations, including uts_ranks, collectives, atomics, rput, dist_object, and others:

/home/data2/upcnightly/dirac/gcc82-EX/work/dbg/upcxx/.nobs/art/ab250a0b85677abfd755255cb89f25e22c05ce28/upcxx/parcel.hpp:365:18: warning: 'void* memcpy(void*, const void*, size_t)' writing to an object of type 'struct main()::<lambda(class upcxx::dist_object<int>&, class upcxx::dist_object<int>&)>' with no trivial copy-assignment; use copy-initialization instead [-Wclass-memaccess]^M
       std::memcpy(y, &x, sizeof(T));^M
       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~^M

[Paul Hargrove]

gcc-8.1 displays the same warnings reported above for 8.2

[Dan Bonachea]

The dirac system has advanced default to g++ 8.2, so this warning is now polluting all our nightly CI test results.

We should really see about fixing this ASAP, to help ensure our Sept release works cleanly with the current g++ release.

Raising priority.

[Amir Kamil]

Fix Issue #158.

→ <<cset d7d3f35fba4c>>

[Paul Hargrove]

Fix confirmed with a config on Dirac very similar to the nightly CI.
Thanks, @akamil