Support for GNU/kFreeBSD

Support for GNU/kFreeBSD

kFreeBSD is GNU (with glibc) on to of a FreeBSD kernel. See
http://glibc-bsd.alioth.debian.org/porting/PORTING

This patch gets Asterisk close to building on Debian kFreeBSD i386,
mainly by adding an extra test for __GLIBC__ in one or two (or more)
places.

OSARCH is set to 'kfreebsd-gnu'

DAHDI support (and support for chan_vpb) was not tested.

Review: https://reviewboard.asterisk.org/r/858/

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@282397 65c4cc65-6c06-0410-ace0-fbb531ad65f3