games/rubix: Drop support for old versions of GCC

Remove code catering to GCC 4.2 (as system compiler) which is not
necessary any longer: USES=compiler never pulls that in any more.

This reverts most of commit 96ec6abecd308e55bbffb19e603b179ebf9a14ab
from 2019 and parts of commit bb2dcea4df840a7acf309b73f5a79c999143e45c
from 2015.