Pass the elfdata pointer in a slot of the temporary TLS area.

Pass the elfdata pointer in a slot of the temporary TLS area.

This is needed to properly initialize the C runtime when libc.so
is loaded by the dynamic linker.

Move the temporary TLS setup before the first system call, just
in case something really horrible happens, we won't crash when
trying to write an error code in 'errno'

Remove the broken TLS_SLOT_THREAD_ID setup. First, this slot
should normally receive the address of a pthread_internal_t,
not a kernel thread identifier. Second, it is never used by
the linker anyway.

Also remove an obsolete comment.