doc about some IRIX 5.3 problems. * doc/posix-functions/getpwnam_r.texi: Mention incompatible declaration on IRIX 5.3. * doc/posix-headers/poll.texi: Mention missing nfds_t on IRIX 5.3. * doc/posix-functions/ptsname.texi: Mention missing declaration on IRIX 5.3. * doc/posix-functions/grantpt.texi: Likewise. * doc/posix-functions/unlockpt.texi: Likewise. * doc/posix-functions/lgamma.texi: Likewise. * doc/posix-functions/nextafter.texi: Likewise. * doc/posix-functions/remainder.texi: Likewise. * doc/posix-functions/select.texi: Mention misplaced declaration on IRIX 5.3. Reported by Tom G. Christensen <tgc@jupiterrise.com>.