ldbl-128ibm-compat: Add argp_error and argp_failure

Use the recently added, internal functions, __argp_error_internal and
__argp_failure_internal, to provide argp_error and argp_failure that can
take long double arguments with IEEE binary128 format on platforms where
long double can also take double format or some non-IEEE format
(currently, this means powerpc64le).

Tested for powerpc64le.

Reviewed-by: Paul E. Murphy <murphyp@linux.ibm.com>