This makes it easier for people to invoke bisect for its usual use cases:

	bisect -compile=loopvar go test

Change-Id: I60ae74f145a2aef7b8d028accc89264e80019d1e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/493856
Run-TryBot: Russ Cox <[email protected]>
Reviewed-by: David Chase <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
gopls-CI: kokoro <[email protected]>