Build infrastructure for elftoolchain tools

Set WITH_ELFTOOLCHAIN_TOOLS in src.conf to use the elftoolchain version
of the following tools:

 * addr2line
 * elfcopy (strip / mcs)
 * nm
 * size
 * strings

Reviewed by:	bapt (earlier version)
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D1224


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275373 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Document ISP 2532 support and hint.isp.0.vports tunable.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275374 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f