Prefer setvbuf() to setlinebuf().

On FreeBSD's libc setlinebuf is a wrapper to setvbuf anyways.

Obtained from:	OpenBSD
MFC after:	5 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275581 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f