This package uses a cdefs.h that originated out of BSD so redefines a lot
of macros normally in BSD's cdefs.h. avoid redefining if those macros
already exist.
Adjust GCC version check to match intention, it was GCC < 2.5 without
__attribute__, not every GCC with a minor below 5!
Patch from Chavdar Ivanov on pkgsrc-users, adjusted to be more conservative
by myself (it's likely some operating systems do need __BEGIN_DECLS!)
PKGREVISION->38 out of paranoia
07b0779508