docs/AddingCustomCompilersOverview.md
This is an overview of what building and adding a compiler to the site looks like, using GCC as an example, but note that the process is similar for all other types of compilers.
/opt/compiler-explorer/gcc-some-version/More info still in Adding a Compiler, and if you can bear listening to Matt, here's a talk about some behind the scenes stuff, with slides online.