From: john stultz <johnstul@us.ibm.com>

Since monotonic_clock() is not defined on every arch yet, this patch
insures the hangcheck-timer module (currently the only user of
monotonic-clock) is not built where it will not compile.

I know, I know. Ideally monotonic_clock() would be implemented on all
arches, but I've just not had the time.  If any of the non x86/x86-64
folks feel bored, drop me a line.  It'd be a fairly easy project.