Filter local variable settings, querying the user if necessary.
VARIABLES is the alist of variable-value settings. This alist is
filtered based on the values of `ignored-local-variables',
`enable-local-eval', `enable-local-variables', and (if necessary)
user interaction. The results are added to
`file-local-variables-alist', without applying them.
If these settings come from directory-local variables, then
DIR-NAME is the name of the associated directory. Otherwise it is nil.