Get automated testing of Checked C compiler tests working again

[dtarditi]

We would benefit from getting automated testing of Checked C compiler tests working again. The targets would be 64-bit hosted compilers running on:

• Linux Ubuntu
• Windows
• MacOS

targeting those platforms. It would be nice to have 32-bit ARM targets tested via emulation because embedded systems are a good community for Checked C. However, we don't have the time/resources to do that.

The main issue is the computation requirements for building the clang compiler. Building the compiler is too computationally intensive for the free tier GitHub Actions or even building within a container on ECS. The choice is either to have a VM in the cloud or a dedicated physical machine. VMs would be expensive unless we implement turning them on and off on demands. MacVMs in the cloud are really expensive, easily costing more than buying a physical Mac device. I'll likely use physical devices running GitHub agents to avoid the costs of the cloud.