[patch] lib/autoconf/specific.m4: turn AC_ISC_POSIX into a NOP

The platform that needed it saw it's last release in 1998,
is completely unsupported since 2006, and it was already
documented that new programs need not use AC_ISC_POSIX.

The main objective of this change is that without it autoupdate
turned AC_ISC_POSIX into AC_SEARCH_LIBS([strerror],[cposix])
in configure.ac, keeping this zombie alive forever.
---
 doc/autoconf.texi        |    5 ++---
 lib/autoconf/specific.m4 |    2 +-
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 2ae8bb9..a4f6666 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
 <at>  <at>  -23411,11 +23411,10  <at>  <at>  See  <at> ref{AC_FUNC_GETMNTENT} and  <at> ref{AC_CHECK_LIB}.
  <at> defmac AC_ISC_POSIX
  <at> acindex{ISC_POSIX}
  <at> ovindex LIBS
-This macro adds  <at> option{-lcposix} to output variable  <at> code{LIBS} if
+This macro added  <at> option{-lcposix} to output variable  <at> code{LIBS} if
 necessary for Posix facilities.  Sun dropped support for the obsolete
 INTERACTIVE Systems Corporation Unix on 2006-07-23.  New programs
-need not use this macro.  It is implemented as
- <at> code{AC_SEARCH_LIBS([strerror], [cposix])} ( <at> pxref{AC_SEARCH_LIBS}).
+need not use this macro.  Since autoconf 2.69 it does nothing.
  <at> end defmac

  <at> defmac AC_LANG_C