...is actually very uncommon in the C world (at least much less common than in the C++ or Rust world).
Specific compilers and stdlibs have specific behaviours which may or may not fully agree with the details written down in the standard. You'll have to pick a subset of compilers you want to support and write your code against that subset of compilers. It's not perfect, but also not much of a problem. It's simply the reality when there are multiple compiler implementations.
In theory, it's really not much different than developing some website that has to run on mobile devices and desktops and all manners of browser implementations and versions and OS and screen sizes and be accessible to screen readers as well. Or is not JavaScript a "language that helps get things done"?
In fact, I'll take the stable, well defined compilers that I can actually test against any day.
...is actually very uncommon in the C world (at least much less common than in the C++ or Rust world).
Specific compilers and stdlibs have specific behaviours which may or may not fully agree with the details written down in the standard. You'll have to pick a subset of compilers you want to support and write your code against that subset of compilers. It's not perfect, but also not much of a problem. It's simply the reality when there are multiple compiler implementations.