[s390] Define a __tls_get_addr macro to avoid declaring it again

[s390] Define a __tls_get_addr macro to avoid declaring it again

commit 050f7298e1ecc39887c329037575ccd972071255 added an extern
declaration for __tls_get_addr that conflicts with the one in s390
dl-tls.h, based on whether __tls_get_addr is defined as a macro.  The
rationale seems to be based on the assumption that __tls_get_addr is
exported for every architecture and hence an internal non-plt alias is
needed.  This is not true for s390 though, since it exports
__tls_get_offset and not __tls_get_addr.  This results in tst-audit9
being stuck in an infinite loop.

This patch fixes this by defining a __tls_get_addr macro to itself so
as to not use the conflicting declaration.