I was merely using the CSS compiler as an example. For something like that, just put a copy in your source repository and forget about it---it'll be fine for a couple of generations of browsers, until the "best current practices" have gone beyond deprecation.
I'm sitting here looking at a JRuby on Rails application using JRuby 1.1.4 and a suitably ancient version of Rails (2.2, maybe?). It's been in production for roughly five years and has received essentially no love during that period; it Just Worked[TM]. The poor sod who was responsible for it and our one other Rails application, our one and only Rails developer, finally managed to move on to other things.
At this point, security issues and (most likely) the inability to slather on new features have percolated up the chain of command and it has been agreed that Something Must Be Done. Since the upgrade path seems to recapitulate the phylogeny of Rails, our options seem to be to rewrite the applications in a modern Rails and kick the can down the street, hoping it'll work better this time, or rewrite it using our common tools around here (and because I've got something to do with it, in the simplest manner possible). (And against the usual "never rewrite anything, ever" meme---which isn't an option---it's going reasonably well.)
As for C, yes, it's feature set has been more-or-less frozen, which is good. It's environment is not. I was reasonably happy with the first version of gcc I used; call it 1.37 or so. Do you think you could use gcc 1.37 today?