Some do, some don't. As I was watching the match, the online bar showed that 30% was in favor of Germany. As Germany started winning and so on, the percentage got higher and higher. Eventually 60% of the online spectators were in favor of Germany. When it comes to foreigners, I think Brazilians root for those they think are playing the best (except for Argentina and maybe USA).
The fact is that Cristiano Ronaldo is a popular figure here, at least, the most known player of all those who were on the field. But as the game moved on and he didn't do anything to help Portugal, people simply chose to root for the best team.
I am one that enjoys a good match. I feel tainted if ever my team wins a game by playing badly or due referee's mistakes. It simply messes with the mood. But the funny thing is that I wasn't sure of which team I was inclined to root in that game. I just wanted it to be a cool game, and it sort of was. Would be even better if Pepe was a better player.
Today, there's Brazil vs Mexico. I do hope it'll be a good fast paced game, not a slowmotion-like game I hate so much.
P.S.: and it all depends on which forefathers you mean. The Netherlands, Germany, Italy...could also take that spot. The Netherlands, when taking down Spain, was playing in the Northeast, which was where that country 'helped colonize' Brazil in the old times. Maybe that's why they felt home, hohoho. Where I live, Portuguese influence is very strong. But something like 200km from here, there are cities where most of people speak german. It's likely that they'll root for a poor country, like the African teams.