Brett, we can use AM_CONDITIONAL() to conditionally enable/disable a feature and AC_CONFIG_FILES() to create a Modules/Setup from a template:

Example:

The conditional

    AM_CONDITIONAL([HAVE_SCPROXY], [test "$ac_sys_system" = "Darwin"])

sets HAVE_SCPROXY_FALSE and HAVE_NIS_SCPROXY based on the check.

On macOS:

    HAVE_SCPROXY_FALSE='#'
    HAVE_SCPROXY_TRUE=''

On Linux:

    HAVE_SCPROXY_FALSE=''
    HAVE_SCPROXY_TRUE='#'

We can either do something like:

    *shared*
    @HAVE_SCPROXY_TRUE@_scproxy _scproxy.c -framework SystemConfiguration -framework CoreFoundation

or:

    *disabled*
    @HAVE_SCPROXY_FALSE*_scproxy