Is there a standard that all software must be developed in ANSI C that I missed, or something? The git developers are saying - we want to use Rust because we think it will save us development effort. NonStop people are saying we can't run this on our platform. It seems to me someone at git made the calculus: the amount that NonStop is contributing is less than what we save going to Rust. Unless NonStop has a support contract with git developers that they would be violating, it seems to me the NonStop people want to have their cake and eat it too.
According to git docs they seem to try to make a best effort to stick to POSIX but without any strong guarantees, which this change seems to be entirely in line with: https://github.com/git/git/blob/master/Documentation/CodingG...
An important point of using C is to write software that adheres to a decades old very widespread standard. Of course developers are free to not do that, but any tiny bit of Rust in the core or even in popular optional code amounts to the same as not using C at all, i.e. only using Rust, as far as portability is concerned.
If your codebase used to conform to a standard and the build environment relies on that standard, and now the your codebase doesn't anymore, then its not the build environment that deviates from the standard, its the codebase that brakes it.