Add native Windows binary for bison.

bison/src/bison/2.4.1/bison-2.4.1-src/m4/double-slash-root.m4

+# double-slash-root.m4 serial 3   -*- Autoconf -*-
+dnl Copyright (C) 2006, 2008 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_DOUBLE_SLASH_ROOT],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_CACHE_CHECK([whether // is distinct from /], [gl_cv_double_slash_root],
+    [ if test x"$cross_compiling" = xyes ; then
+        # When cross-compiling, there is no way to tell whether // is special
+        # short of a list of hosts.  However, the only known hosts to date
+        # that have a distinct // are Apollo DomainOS (too old to port to),
+        # Cygwin, and z/OS.  If anyone knows of another system for which // has
+        # special semantics and is distinct from /, please report it to
+        # <bug-gnulib@gnu.org>.
+        case $host in
+          *-cygwin | i370-ibm-openedition)
+            gl_cv_double_slash_root=yes ;;
+          *)
+            # Be optimistic and assume that / and // are the same when we
+            # don't know.
+            gl_cv_double_slash_root='unknown, assuming no' ;;
+        esac
+      else
+        set x `ls -di / // 2>/dev/null`
+        if test "$[2]" = "$[4]" && wc //dev/null >/dev/null 2>&1; then
+          gl_cv_double_slash_root=no
+        else
+          gl_cv_double_slash_root=yes
+        fi
+      fi])
+  if test "$gl_cv_double_slash_root" = yes; then
+    AC_DEFINE([DOUBLE_SLASH_IS_DISTINCT_ROOT], 1,
+      [Define to 1 if // is a file system root distinct from /.])
+  fi
+])