cmd/guru: report 'whicherrs' in modes of 'what' query

A 'what' query reports which other query modes are applicable to the
selected syntax.  A 'whicherrs' query is similar to a 'pointsto'
query, so we enable it using the same criteria.

Fixes issue golang/go#18938

Change-Id: Iae062e0c933c7764bc335488adabf816d63ac837
Reviewed-on: https://go-review.googlesource.com/37349
Reviewed-by: Dominik Honnef <dominik@honnef.co>
1 file changed