langinfo, nl_langinfo: Fix for IRIX 5.3. * m4/langinfo_h.m4 (gl_LANGINFO_H): Test whether langinfo.h defines T_FMT_AMPM, YESEXPR. Set HAVE_LANGINFO_T_FMT_AMPM, HAVE_LANGINFO_YESEXPR. * modules/langinfo (Makefile.am): Substitute HAVE_LANGINFO_T_FMT_AMPM, HAVE_LANGINFO_YESEXPR. * lib/langinfo.in.h (T_FMT_AMPM, GNULIB_defined_T_FMT_AMPM): Define if HAVE_LANGINFO_T_FMT_AMPM is 0. (YESEXPR, NOEXPR, GNULIB_defined_YESEXPR): Define if HAVE_LANGINFO_YESEXPR is 0. * lib/nl_langinfo.c (rpl_nl_langinfo): Handle also T_FMT_AMPM, YESEXPR, NOEXPR. * doc/posix-headers/langinfo.texi: Mention the IRIX 5.3 problem. * doc/posix-functions/nl_langinfo.texi: Likewise. Reported by Eric Blake.