Analyzer diagnostics for uninstantiated classes

Hi,

clang's analyzer doesn't seem to emit diagnostics for uninstantiated
classes. Can I as a frontend user turn these on with some flag?

The current situation is a little unfortunate when developing library code: the
library might not instantiate all its types while in user code the definitions
of all functions might not be available.

I see this behavior e.g. in r192680.

Example:

    struct A {
      void setup() { n = N; }
      A() {
        setup();
        N = 1;
      }

      int N, n;
    };

    int main() {
      //A a; // **HERE**
    }

With the line marked **HERE** commented out `clang --analyze` finds nothing,
while with it active I get what I wanted:

    test.cpp:2:20: warning: Assigned value is garbage or undefined
      void setup() { n = N; }
                       ^ ~
    1 warning generated

What awesome times were I am surprised by this kind problem, thanks for the
great work,

Benjamin