if you allow me my 2 cents:
At configure time, it is possible to distinguish between several
different user inputs:
- the user typed --enable-foo,
- the user typed --disable-foo or --enable-foo=no,
- the user typed --enable-foo=ARG (ARG is available for further
- the user used none of the above.
IIUC you have already sorted out the visibility issue by using the last,
and the memchecker issue is about having an incompatible version
installed. One typical semantics would be to not try to use the feature
at all if --disable-foo was explicitly passed.
Hope that helps.