SPMI: Native Linux-hosted throughput runs #85749

SPMI currently uses Windows-hosted cross-jits for measuring throughput on the Linux collections. This relies on MSVC produced code being a good proxy for clang-produced code. That's probably the case for many "semantic" changes in the JIT, but for many low-level optimizations (e.g. #85144) it might not be. This work item is about expanding superpmi-diffs to do native Linux-hosted SPMI runs when measuring throughput.