I'm told my prefix work-around wasn't enough to make it compile,
although I'm not sure why; I did some basic testing and that
approach appeared to work, but I'm not in a position to do a
full compile on CentOS 6 so I can't be sure of anything.
I have had it confirmed that the additional change to not use
named initialisers is enough to make it compile, so let's
throw that into the mix too.
Ancient versions of gcc (pre 4.6) can't directly initialise
members of anonymous inner unions/structs by name.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676
Unfortunately, RHEL 6 shipped with one of these ancient
versions and so we're stuck with it until approximately the
heat death of the universe.
Putting explicit braces into the initialisation is possibly a
work-around but the behaviour there was never fully understood
before direct initialisation was made to work.
So, this may or may not work.