Add stronger checking

- Add assertions to enforce that objects are of the correct kind and
  have been allocated.

- Make destructors check if objects have been allocated before
  deleting.

- Operations that require a non-NullDevice return failure if given a
  NullDevice.

- Use static_cast rather than reinterpret_cast when cohersing from a
  base class to a derived class.

Change-Id: I02ee0ea9d7982fd7ca29d49c9b02cfae111b7127

rocclr/device/gpu/gpuprogram.hpp

@@ -349,6 +349,7 @@ class Program : public NullProgram {
 
   //! Return a typecasted GPU device
   gpu::Device& gpuDevice() {
+    assert(!isNull());
     return const_cast<gpu::Device&>(static_cast<const gpu::Device&>(device()));
   }
 
@@ -476,6 +477,7 @@ class HSAILProgram : public device::Program {
 
   //! Return a typecasted GPU device. The device must not be the NullDevice.
   gpu::Device& gpuDevice() {
+    assert(!isNull());
     return const_cast<gpu::Device&>(static_cast<const gpu::Device&>(device()));
   }