cmd/compile,go/build,internal/cpu: gofmt

I don't know why these files were not formatted. Perhaps because
their changes came from Github PRs?

Change-Id: Ida8d7b9a36f0d1064caf74ca1911696a247a9bbe
Reviewed-on: https://go-review.googlesource.com/114824
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/go/build/build_test.go

@@ -177,7 +177,7 @@ func TestShouldBuild(t *testing.T) {
 }
 
 func TestGoodOSArchFile(t *testing.T) {
-	ctx := &Context{BuildTags: []string{"linux"}, GOOS:"darwin"}
+	ctx := &Context{BuildTags: []string{"linux"}, GOOS: "darwin"}
 	m := map[string]bool{}
 	want := map[string]bool{"linux": true}
 	if !ctx.goodOSArchFile("hello_linux.go", m) {