cmd/link: short tests are not short enough

Running all.bash (which does go test -short std cmd), my target is usually that individual tests should run in under 1 second.
	
The cmd/link test takes 3.4s on my system. Can we make it take less time?

cmd/link is implicitly tested by pretty much every other test in the system, so it's hard to believe it needs to do a ton in the -short test.

/cc @aclements