cmd/vet: reported typecheck errors not sorted by file position

[rsc]

Compare gc and vet typecheck errors:

$ go test
# golang.org/x/vgo2/vendor/cmd/go/internal/modfetch [golang.org/x/vgo2/vendor/cmd/go/internal/modfetch.test]
./coderepo.go:279:70: undefined: file2
./coderepo.go:294:8: no new variables on left side of :=
./coderepo.go:294:30: undefined: gomod
# golang.org/x/vgo2/vendor/cmd/go/internal/modfetch
./coderepo.go:294:30: undeclared name: gomod
./coderepo.go:294:8: no new variables on left side of :=
./coderepo.go:279:70: undeclared name: file2
vet: typecheck failures

(go test printing both sets at all is a different issue, but it is nice for seeing how they compare.)

It's weird that the errors from vet come out not sorted in file line order. They should.