MINOR: config: make cfg_eval_condition() support predicates with arguments

MINOR: config: make cfg_eval_condition() support predicates with arguments

Now we can look up a list of known predicates and pre-parse their
arguments. For now the list is empty. The code needed to be arranged with
a common exit point to release all arguments because there's no default
argument freeing function (it likely only used to exist in the deinit
code). Since we only support simple arguments for now it's no big deal,
only a 2-liner loop.