regex(3): Add support for \< and \> word delimiters

Solaris and other OSs have support for \< and \> as word
delimiters in utilities like sed(1). These are useful to
have for general compatiblity with Solaris but should be
avoided for portability with other systems, including the
traditional BSDs.

Bump __FreeBSD_version as this is likely to affect some
userland utilities.

Reference:
https://www.illumos.org/issues/516

PR:		bin/153257
Obtained from:	Illumos
MFC after:	1 month