Remove <libc-tsd.h>

Remove <libc-tsd.h>

Use __thread variables directly instead.  The macros do not save any
typing.  It seems unlikely that a future port will lack __thread
variable support.

Some of the __libc_tsd_* variables are referenced from assembler
files, so keep their names.  Previously, <libc-tls.h> included
<tls.h>, which in turn included <errno.h>, so a few direct includes
of <errno.h> are now required.

Reviewed-by: Frédéric Bérat <fberat@redhat.com>