Add a virtual destructor to cprover_exception_baset

While exceptions under normal usage scenarios don't need a virtual destructor
(when an exception is thrown, it is the runtimes responsibility to properly
destroy it, and it does know the type of the exception at the point where it's
thrown), it is just generally good practice to have virtual destructors in base
classes to accomodate for situations where a polymorphic destruction may be
needed.

Author: hannes-steffenhagen-diffblue

src/util/exception_utils.h

@@ -16,13 +16,18 @@ Author: Fotis Koutoulakis, fotis.koutoulakis@diffblue.com
 /// Base class for exceptions thrown in the cprover project.
 /// Intended to be used as a convenient way to have a
 /// "catch all and report errors" from application entry points.
+/// Note that the reason we use a custom base class as opposed to
+/// std::exception or one of its derivates to avoid them being accidentally
+/// caught by code expecting standard exceptions to be only thrown by the
+/// standard library.
 class cprover_exception_baset
 {
 public:
   /// A human readable description of what went wrong.
   /// For readability, implementors should not add a leading
   /// or trailing newline to this description.
   virtual std::string what() const = 0;
+  virtual ~cprover_exception_baset() = default;
 };
 
 /// Thrown when users pass incorrect command line arguments,