Backport AC_PATH_PROGS_FEATURE_CHECK

In order to allow working with older versions of autoconf we backport
this macro, but only if it's not defined already (by autoconf itself).

This commit can be reverted after we decide support for autoconf 2.61
and below should be deprecated.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

autotools/ac_path_progs_feature_check.m4

+# Backport of AC_PATH_PROGS_FEATURE_CHECK from autoconf 2.64
+# (available since version 2.62)
+#
+# The following code comes from lib/autoconf/programs.m4,
+# in the autoconf 2.64 source code. Its copyright is:
+
+#
+# Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
+# 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software
+# Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+# As a special exception, the Free Software Foundation gives unlimited
+# permission to copy, distribute and modify the configure scripts that
+# are the output of Autoconf.  You need not follow the terms of the GNU
+# General Public License when using or distributing such scripts, even
+# though portions of the text of Autoconf appear in them.  The GNU
+# General Public License (GPL) does govern all other use of the material
+# that constitutes the Autoconf program.
+#
+# Certain portions of the Autoconf source text are designed to be copied
+# (in certain cases, depending on the input) into the output of
+# Autoconf.  We call these the "data" portions.  The rest of the Autoconf
+# source text consists of comments plus executable code that decides which
+# of the data portions to output in any given case.  We call these
+# comments and executable code the "non-data" portions.  Autoconf never
+# copies any of the non-data portions into its output.
+#
+# This special exception to the GPL applies to versions of Autoconf
+# released by the Free Software Foundation.  When you make and
+# distribute a modified version of Autoconf, you may extend this special
+# exception to the GPL to apply to your modified version as well, *unless*
+# your modified version has the potential to copy into its output some
+# of the text that was the non-data portion of the version that you started
+# with.  (In other words, unless your change moves or copies text from
+# the non-data portions to the data portions.)  If your modification has
+# such potential, you must delete any notice of this special exception
+# to the GPL from your modified version.
+#
+# Written by David MacKenzie, with help from
+# Franc,ois Pinard, Karl Berry, Richard Pixley, Ian Lance Taylor,
+# Roland McGrath, Noah Friedman, david d zuhn, and many others.
+#
+# The code was modified by ultrotter@google.com, adding surrounding ifdefs.
+
+m4_ifdef([AC_PATH_PROGS_FEATURE_CHECK],,
+  m4_define([AC_PATH_PROGS_FEATURE_CHECK],
+  [_$0([$1], [$2], [$3], m4_default([$4], [:]), [$5])dnl
+  ]))
+
+m4_ifdef([_AC_PATH_PROGS_FEATURE_CHECK],,
+  m4_define([_AC_PATH_PROGS_FEATURE_CHECK],
+  [if test -z "$$1"; then
+    ac_path_$1_found=false
+    # Loop through the user's path and test for each of PROGNAME-LIST
+    _AS_PATH_WALK([$5],
+    [for ac_prog in $2; do
+      for ac_exec_ext in '' $ac_executable_extensions; do
+        ac_path_$1="$as_dir/$ac_prog$ac_exec_ext"
+        AS_EXECUTABLE_P(["$ac_path_$1"]) || continue
+  $3
+        $ac_path_$1_found && break 3
+      done
+    done])dnl
+    if test -z "$ac_cv_path_$1"; then
+      m4_default([$4],
+        [AC_MSG_ERROR([no acceptable m4_bpatsubst([$2], [ .*]) could be dnl
+  found in m4_default([$5], [\$PATH])])])
+    fi
+  else
+    ac_cv_path_$1=$$1
+  fi
+  ]))
+