swift234

Fix <rdar://problem/21429694> QoI: diagnostic for accessing private methods could be improved

When member lookup completely fails and when CSDiags is the one performing
the lookup, reissue another lookup that ignores access control.  This allows
it to find inaccessible members and diagnose them as such, instead of pretending
we have no idea what the user wants.  We now produce an error message like this:

main.swift:1:6: error: 'foo' is inaccessible due to 'private' protection level
 C().foo()
     ^
test.swift:1:35: note: 'foo' declared here
  internal class C { private func foo() {} }
                                  ^

instead of:

main.swift:1:2: error: value of type 'C' has no member 'foo'
 C().foo()
 ^~~ ~~~