RFC: TLS improvements for IA32 and AMD64/EM64T

[Roland McGrath]

> The patch also adds a test to fix a problem I ran into while testing
> these optimizations, that turned out to be possible to trigger with
> the old code.
> 
> It also introduces one missing initial-exec annotation to a data
> symbol, removing code size differences between the dynamic loaders.

These sound like fixes that need to be considered independent of your
proposed ABI additions.  Please post separately each of those patches with
some elaboration on the need for it.


Thanks,
Roland