Declare default virtual destructors to quiet [-Wnon-virtual-dtor]

[bashi-bazouk]

This change allows compiling ComTests.cpp and ResourceTests.cpp with -Werror -Wnon-virtual-dtor enabled.

[dunhor]

I get that these types are just for unit tests, but these are all COM types where the destructor really shouldn't be part of the v-table because the type destroys itself in the Release method. If these warnings are causing issue, we should disable them either globally or locally at their definitions

[jonwis]

This should be ~IDerivedTest - you can't declare a destructor for a base type.

[jonwis]

Same as above; s/b ~IDerivedTestInspectable

[jonwis]

In a earlier project, we kept finding leaks when someone had the pattern class CIntermediate : IFooExtendsIUnknown then class CDerivedMost : CIntermediate where the CDerivedMost overrode a method on IFooExtendsIUnknown and added additional state. The delete this in CIntermediate::Release didn't trigger ~CDerivedMost because nobody had a virtual ~Anything() in the type hierarchy. The super easy fix was to just add virtual ~CIntermediate() { }; and all the leaks got closed.

So I'm sympathetic to the warning. Should it be firing for types that contain only types with trivial destructors, though? Like the FakeStream type has no state to destroy and no members with nontrivial destructors.

So the two that need it in this change are the IUnknownFake (an instance with non-pure-virtual methods) and FakeStream. The others are just "pure interfaces."