Auto merge of #109073 - michaelwoerister:limit-mingw-llvm-link-jobs, …

…r=Mark-Simulacrum

Limit the number of parallel link jobs during LLVM build for mingw.

This PR is an attempt to unblock rust-lang/rust#108355, which keeps failing while trying to link various LLVM artifacts on mingw runners. It looks like doing too many linking jobs might put too much load on the system? (Although I don't understand why the jobs are only failing for #108355 while they seem to pass for others)

r? infra-ci