23.3.1 Non-interactive behavior
Autoconf's generated `configure' scripts are designed to be
non-interactive -- they should not prompt the user for input. Many
users like the fact that `configure' can be used as part of a
automated build process. By introducing code into `configure'
which prompts a user for more information, you will prohibit unattended
operation. Instead, you should use the
AC_ARG_ENABLE macro in
`configure.in' to add extra options to `configure' or consider
runtime configuration (see section 23.3.2 Testing system features at application runtime).