Whitespace

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Style: prefer implicit this, having {}, nullptr

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Fixed tests: universe->heap was removed.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
write_barrier: move cond. compilation into macro

Avoid these kind of #if conditional compilation for more idomatic code.

Signed-off-by: Stefan Marr <git@stefan-marr.de>