langinfo, nl_langinfo: Fix for IRIX 5.3.

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.