WII: Fix Gamecube build. Compiler prefix change for r26 SDK missed.

The previous update to the Wii configure sections including changing
the compiler prefix missed changing the Gamecube section.
WII: Fix Gamecube build. Missing ifdef guard for Wii DVD interface.
WII: Another fix for Gamecube build. Corrected Disc Interface object.
WII: Add missing dvd interface header for Gamecube build.