configure: Check that "libtool" is not the MacOSX one

The "libtool" binary on MacOSX is not GNU libtool, and doesn't support
anything like the same set of command line options. Test whether we
have accidentally picked this up (by looking for whether it handles
the GNU --version switch), and discard it if so. The fallback machinery
for the "we don't have a libtool" case will work fine. This fixes a
failure in "make install" on MacOSX.
Reported-by: NPeter Cheung <mcheung63@hotmail.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1367701071-6630-1-git-send-email-peter.maydell@linaro.org
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -1685,6 +1685,14 @@ if ! has $libtool; then
     libtool=
 fi
 
+# MacOSX ships with a libtool which isn't the GNU one; weed this
+# out by checking whether libtool supports the --version switch
+if test -n "$libtool"; then
+  if ! "$libtool" --version >/dev/null 2>&1; then
+    libtool=
+  fi
+fi
+
 ##########################################
 # Sparse probe
 if test "$sparse" != "no" ; then