Confirm if local cpu is cause of slow compiles; if so, upgrade

[Venryx]

See here for more info (including some time-passes data): #285 (comment)

Note: The slowdown could also be some side-effect of being on Windows. (for one, it means the mold linker isn't in use; but even beyond that, there may be other negative compile-time side-effects, eg. NTFS slowness, antivirus software/components, etc.)