vma-iter: Improvements for BSD platforms. - Add support for GNU/kFreeBSD. - Make it work on FreeBSD and NetBSD even when /proc is not mounted. - Speed up on OpenBSD. * lib/vma-iter.c (struct rofile, rof*): Define also on GNU/kFreeBSD. (vma_iterate_bsd): New function. (vma_iterate): Use it as fallback on FreeBSD and NetBSD. Use it as first choice on OpenBSD. Treat GNU/kFreeBSD like Linux. * lib/vma-iter.h (VMA_ITERATE_SUPPORTED): Define also on GNU/kFreeBSD. * modules/vma-iter (configure.ac): Require AC_C_INLINE.