configure: Fix warnings on CentOS and bump the minimum autoconf version

* configure.ac: Bump the minimum version to 2.60 as needed by
  AC_USE_SYSTEM_EXTENSIONS.  AC 2.60 is nearly 10 years old, note.  Add
  AC_PROG_RANLIB, for when --disable-shared is used.

  There are other warnings on, e.g., CentOS 6.7 with 2.63, but they
  don't go away if the suggestion to add AC_SYSTEM_EXTENSIONS is
  followed. This warning doesn't occur on Fedora with AC 2.69.

  Note: autoconf (and other auto*) should only be needed on developer
  machines building direct from git.  Other systems should be using the
  'make dist' tarballs, with a ready-made build system, that does not
  need auto* intalled.

(cherry picked from commit f9f4731245eb9f83d0795acac24183c6cf709288)

diff --git a/configure.ac b/configure.ac
index ff340f0973a93c904cd304f0bf06ab3e53921c3d..fa519a59a89d3ed9279884a570d9c03c6cdd22f0 100755 (executable)
--- a/configure.ac
+++ b/configure.ac
@@ -5,7 +5,7 @@
 ##  Copyright (c) 1996, 97, 98, 99, 2000 Kunihiro Ishiguro <kunihiro@zebra.org>
 ##  Portions Copyright (c) 2003 Paul Jakma <paul@dishone.st>
 ##
-AC_PREREQ(2.53)
+AC_PREREQ(2.60)
 
 AC_INIT(Quagga, 0.99.23.1+cl3u2, [https://bugzilla.quagga.net])
 AC_CONFIG_SRCDIR(lib/zebra.h)
@@ -81,6 +81,7 @@ AC_LANG([C])
 AC_PROG_CC
 AC_PROG_CPP
 AM_PROG_CC_C_O
+AC_PROG_RANLIB
 AC_PROG_EGREP
 
 dnl autoconf 2.59 appears not to support AC_PROG_SED