alt Hacker Newsit's not that simple. you want to be able to use a modern toolchain (compilers that support the latest standards) but build a binary that runs on older systems.
the only way to achieve that is to get the older libraries installed on a newer system, or you could try backporting the new toolchain to the older system. but that's a lot harder.
It may be hard-ish, sometimes. Sometimes it's a breeze. And sometimes you can just use host's toolchain with container's sysroot and proceed as if you were cross-compiling. Most of the time it's not a big deal.