gallium: use Haiku provided debug_printf in OS.h

Signed-off-by: Brian Paul <brianp@vmware.com>

src/gallium/auxiliary/util/u_debug.h

@@ -91,8 +91,11 @@ debug_printf(const char *format, ...)
    (void) format; /* silence warning */
 #endif
 }
+#else /* is Haiku */
+/* Haiku provides debug_printf in libroot with OS.h */
+#include <OS.h>
+#endif
 
-#endif /* !PIPE_OS_HAIKU */
 
 /*
  * ... isn't portable so we need to pass arguments in parentheses.