ddraw/tests: Fix compilation on systems that don't support nameless unions.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=6710

Your paranoid android.


=== W98SE (32 bit dsurface) ===
dsurface: unhandled exception c0000005 at 00415109