Rather than list broad open ranges of supported compilers, we should list compiler versions (and possibly polyfill versions) that we have tested.

We could adapt the internal matrix of compiler/polyfill versions we're developing and present it as a table on our docs site.

We'll need to think about what level of granularity to present, e.g. do we list every version of gcc we've tried or do we list just what we use in our CI system? The latter seems more manageable and is a better representation of what we're making sure stays working.