build/CI/packaging: lower the required Autoconf version back to 2.63

Author: akopytov

configure.ac

@@ -1,6 +1,6 @@
 # Process this file with autoconf to produce a configure script.
 
-AC_PREREQ([2.70])
+AC_PREREQ([2.63])
 AC_INIT([sysbench],[1.1.0],[https://github.com/akopytov/sysbench/issues],[sysbench],[https://github.com/akopytov/sysbench])
 AC_CONFIG_AUX_DIR([config])