Compilers typically don't use multiple cores, but the build system that invokes them do, by invoking them in parallel. Modern build systems will typically invoke commands for 1 target per core, which means that on my system for example, building my software uses all 16 cores more or less until the final steps of the process.

The speed record for building my software is held by a system with over 1k cores (a couple of seconds, compared to multiple minutes on a mid-size Threadripper).