None really, compilation is considered a branch/integer workload and has been that way for decades. Its a lot of tree traversals, and short string manipulation. One of the bigger boosts in recently memory were the "fast strings (rep mov*)" implementations about 10 years ago.

Single core compilation is actually a fairly good metric for general purpose performance. Of course it scales almost linearly with core count too.

Regarding the speed of compilation, I'm not sure which if any recent ISA extensions matter.

What matters to me is the ISA extensions that are needed by the software I'm building, typically DL or HPC code. Life is easier when I can build and test the software on my local machine, without having to involve some fancy new server.