Due to a libz dependency in some distro's binutils package,
C++ demangle support isn't compiled in despite the necessary
libraries being available.

Fix this by adding a -lz link test to the dependency detection
rules.
Signed-off-by: NMike Galbraith <efault@gmx.de>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1249733655.6929.5.camel@marge.simson.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>