HP-UX

The idea is more get GCC working even if not the latest, because believe me it is not that obvious to compile from scratch with all the dependencies...
Even with HP depot you will have to solve the dependencies in some cases, like gcc.. that is why I gave you what you need to install first and in that order.. once you have a GCC compiler working ist up to you after if you wish to install from sources but if you never have done such, it it wise to start and have something that works, lest say you managed to install gcc by other means, when you will be trying to compile a new product and see something go wrong when you have typed "configure", wherewill you start searching? could it be you are missing C libraries? some dependencies form other sources? (It happens to me now I have no more HP (shame...) and see copies (yes...) of binaries on AIX where depending what I do, fail, and I have to trace EVERYTHING to see what is missing and spend weeks to get all working, because yes it can work and suddenly you compile using THE library from a dependency you did not need at the beginning and you are done...
So get your environment working first with ALL the needed tools to achieve your goals, then with peace of mind, you know when installing, failures are of other nature than missing a bit of soft ( well could be $PATH etc but you know you have it somewhere...) in most cases after its a question of ENV... ( and very rarely but could happen: kernel parameters...)

vbe, looks like I got a typo on my reply. I meant to say, I will be following your advice. And yes your logic is sound in what you say. Apologies for mistyping. Basically I agree with everything you have said, and "I WILL BE" following your advice