[analyzer] Reduce parallel code paths in SimpleSValBuilder::evalBinOpNN, and handle...

[analyzer] Reduce parallel code paths in SimpleSValBuilder::evalBinOpNN, and handle mixed-type operations more generally.

The logical change is that the integers in SymIntExprs may not have the same type as the symbols they are paired with. This was already the case with taint-propagation expressions created by SValBuilder::makeSymExprValNN, but I think those integers may never have been used. SimpleSValBuilder should be able to handle mixed-integer-type SymIntExprs fine now, though, and the constraint managers were already being defensive (though not entirely correct). All existing tests pass.

The logic in evalBinOpNN has been simplified so that conversion is done as late as possible. As a result, most of the switch cases have been reduced to do the minimal amount of work, delegating to another case when they can by substituting ConcreteInts and (as before) reversing the left and right arguments when useful.

Comparisons require special handling in two places (building SymIntExprs and evaluating constant-constant operations) because we don't /know/ the best type for comparing the two values. I've approximated the rules in Sema [C99 6.3.1.8]  but it'd be nice to refactor Sema's actual algorithm into ASTContext.

This is also groundwork for handling mixed-type constraints better than we do now.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156270 91177308-0d34-0410-b5e6-96231b3b80d8