TriBITS not catching a circular dependency between a subpackage and its parent package

[bartlettroscoe]

Description

The PR trilinos/Trilinos#1142 where the thyra/core/cmake/Dependencies.cmake file was updated to list a dependence of ThyraCore on its parent package Thyra shows that there is a missing check in TriBITS for an attempt to define a circular dependence of a subpackage on its parent package. (Because there is automatically a dependence of the parent package on eadh of its subpackages.)