limited to gcc5 because others do not seem to run into the same issues, to
avoid a regression for them.
disable libssp on netbsd - it conflicts with native libssp
(related: PR pkg/47213)
Use a more sane specfile for netbsd, linking against libc when building
shared.
bump gcc47 PKGREVISION
bump gcc47-libs PKGREVISION further than gcc47