[aprdm]

Oh yeah, it is certainly possible.

you have build_requires which you can list dependencies that you require at build time (e.g: gcc-3 vs gcc-4) but not at runtime.

So you can have things that were built with gcc-3 and gcc-4 running side by side in a same shell environment without issues.

gcc itself, in this case, would be a rez package that can have multiple versions installed in the system.