Small fix after 80ad7cf8 to fix ticket #1870.

Ken Raffenetti reported the default GNU patch for FreeBSD is too old to
recognise the --no-backup-if-mismatch flag. This fix switches to a manual
removal approach.
Signed-off-by: Ken Raffenetti <raffenet@mcs.anl.gov>

autogen.sh

@@ -919,7 +919,8 @@ if [ $do_bindings = "yes" ] ; then
     echo "------------------------------------------------------------------------"
     echo
     echo_n "Patching libtool.m4 for compatibility with nagfor shared libraries... "
-    patch --forward --no-backup-if-mismatch -p0 -s -l < maint/libtool.m4.patch
+    patch --forward -p0 -s -l < maint/libtool.m4.patch
+    rm -f confdb/libtool.m4.orig
     if [ $? -eq 0 ] ; then
         echo "done"
     else