[Bug other/58319] explicit cast doesn't disable -Wconversion warning.

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58319

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
You can ensure the value is not too large for the target:

        X x = { .field = ( u & (-1u >> 1) ) };