[PATCH] Improve performance of libc locks

[Wilco Dijkstra]

 Hi Carlos,

> This impacts all architectures.

That was the goal indeed - we should add single-threaded optimizations in a
generic way.

> If we don't have a benchmark that shows this specific base of ST vs MT and
> internal __libc_lock_lock-locks then we should add one. Improving the internal
> locking for our algorithms is always going to be a point of interest for IHVs.

I can easily wrap my rand() microbench in json and add it to the benchtests.
I think it would be harder to do more tests on internal locks/headers since they
are not easily usable from benchtest infrastructure (just including libc-lock.h
results in lots of errors...).

Cheers,
Wilco