libc-internal thread-specific data revamp

[Roland McGrath]

> Roland McGrath <roland@frob.com> writes:
> 
> > The following patches revamp the facilities for libc-internal
> > thread-specific data used by malloc and the dynamic linker.
> 
> Thanks, I've applied the patch.

Great!

> The only place where I can see possible problems is with replacing the
> weak undefined symbols with the .bss/.data trick.  It works for all
> platforms we are currently interested in and here only since we don't
> support dynamically loading libpthread.  So it's in for now but we
> should keep the eyes open for possible situations where this leads to
> problems.

Indeed we should be on the look-out, but I am not concerned.  Fortunately,
the new interface makes this an implementation detail that only the
bits/libc-tsd.h implementation for a particular platform needs to know.