Minor changes to reduce warnings seen when using gfxreconstruct,
no (intentional) functional changes.

Using struct as in the definition for forward declaration of the
ReplayDeviceInfo tag (clang -Wmismatched-tags)

Explicitely define assignment operators for clang
 -Wdeprecated-copy-with-user-provided-copy warning.
  clang output:
> definition of implicit copy assignment operator for 'ShaderDescriptorInfo'
> is deprecated because it has a user-provided copy constructor