In some places we used $DEVKITARM, but in others we hardcode the path
$DEVKITPRO/devkitARM. To ensure consistent behavior, I changed it to the
latter everywhere for now. Should it turn out that we really want to
have this flexible, we can reintroduce $DEVKITARM in a proper way. In
that case, we could augment configure to set DEVKITARM to
$DEVKITPRO/devkitARM, if it has not been set yet.