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
https://newtestbot.winehq.org/JobDetails.pl?Key=3061

Your paranoid android.


=== w864 (32 bit ddraw2) ===
ddraw2: unhandled exception c0000005 at 00420E52

=== w864 (32 bit ddraw1) ===
ddraw1: unhandled exception c0000005 at 0041212F