[patch] Make std::tr1::shared_ptr thread-safe.

[Paolo Carlini]

Ulrich Drepper wrote:

> This patch looks like a terrible idea.  If it's intended as an interim
> step, perhaps, but this should be handled using atomic operations alone.

Thanks for your feedback: indeed (see the thread on libstdc++) the issue
is now becoming more clear. Our current plans are (I think): in the
4.0.0 time frame providing a stop-gap solution as outlined by Alexander
and Peter.

Then, readd to the library implementations of exchange_and_add for the
platforms that can implement it, otherwise fall back to the stop-gap
solution (some configury bits needed).

Thanks,
Paolo.