[PATCH] Use __attribute__((tls_model(""))), add hidden aliases to TLS vars

[Roland McGrath]

Cool, I'll put that in.  I was going to get to that myself but hadn't yet
installed the compiler that supports it.

It occurs to me you could use libc_hidden_proto instead of macros.
But that is uglier in the asm, and both ways do the same thing.

One thing that concerns me is if a program (erroneously) does 
"__thread int errno;" (sans extern) or suchlike.  Then the program
and libpthread will use its errno, but libc will only set __libc_errno.

It would be nice if this produced a link-time error like a multiple
definition with a non-shared object would.  But AFAIK no .so symbol will
ever produce a multiple definition error.  Perhaps we could do some hack in
the linker script.