ccan: Only build ccan-failtest when we are in developer mode

ccan: Only build ccan-failtest when we are in developer mode

From: Andrew Bartlett <abartlet@samba.org>

This code is incredibly useful, but is only needed in test code and may not be
perfectly portable.  It has compiled on all systems bar Solaris so far, but
rather than make it a requirement to build Samba, just keep it for development.

Andrew Bartlett

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Autobuild-User(master): Rusty Russell <rusty@rustcorp.com.au>
Autobuild-Date(master): Thu Jun  7 18:53:12 CEST 2012 on sn-devel-104