setpayloadsig*: Support newer MIPS CPUs. * lib/setpayloadsig.c (setpayloadsig): On MIPS CPUs with MIPS_NAN2008_DOUBLE, reject a zero payload. * lib/setpayloadsigf.c (setpayloadsigf): On MIPS CPUs with MIPS_NAN2008_FLOAT, reject a zero payload. * lib/setpayloadsigl.c (setpayloadsigl): On MIPS CPUs with MIPS_NAN2008_LONG_DOUBLE, reject a zero payload.