libstdc++/7445: poor performance of std::locale::classic() in multi-threaded applications

[Benjamin Kosnik]

Sorry about the delay. My redhat.com email got completed screwed. This
post may or may not work.

> I hereby propose that the PR patch and all follow-on patches be
> unrolled until someone produces a real test case that performs poorly.
> Performance patches produced by code inspection should hold no merit
> with us.

Sounds good. 

I think that locale::classic is wrapped with locale::_S_initialize.
That's what should be called first, before classic. Perhaps the problem
lies there.

-benjamin