RFC: TLS improvements for IA32 and AMD64/EM64T

[Roland McGrath]

The fixes really need to be separate from ABI additions, sorry.  If the
fixes are worthwhile, they should not wait.  Any ABI changes require
further study and consideration, and I anticipate their details may change
substantially before we conclude on something new for TLS ABIs.  As a
general rule, multiple smaller patches for the separable issues are always
the best way to get changes merged in sooner.  This is not new.


Thanks,
Roland