go/types: migrate importer usage in tests

To use an importer that knows where to find stdlib .a files based on
their new locations once the checked-in .a files are removed.

Change-Id: I981812306b3512380d58cb0f599a9a61b27ba0d7
Reviewed-on: https://go-review.googlesource.com/c/go/+/442695
Reviewed-by: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/go/types/issues_test.go

@@ -578,6 +578,8 @@ func TestIssue44515(t *testing.T) {
 func TestIssue43124(t *testing.T) {
 	// TODO(rFindley) move this to testdata by enhancing support for importing.
 
+	testenv.MustHaveGoBuild(t) // The go command is needed for the importer to determine the locations of stdlib .a files.
+
 	// All involved packages have the same name (template). Error messages should
 	// disambiguate between text/template and html/template by printing the full
 	// path.

src/go/types/self_test.go

@@ -9,6 +9,7 @@ import (
 	"go/importer"
 	"go/parser"
 	"go/token"
+	"internal/testenv"
 	"path"
 	"path/filepath"
 	"testing"
@@ -18,6 +19,8 @@ import (
 )
 
 func TestSelf(t *testing.T) {
+	testenv.MustHaveGoBuild(t) // The Go command is needed for the importer to determine the locations of stdlib .a files.
+
 	fset := token.NewFileSet()
 	files, err := pkgFiles(fset, ".")
 	if err != nil {
@@ -32,6 +35,8 @@ func TestSelf(t *testing.T) {
 }
 
 func BenchmarkCheck(b *testing.B) {
+	testenv.MustHaveGoBuild(b) // The Go command is needed for the importer to determine the locations of stdlib .a files.
+
 	for _, p := range []string{
 		"net/http",
 		"go/parser",

src/go/types/sizes_test.go

@@ -12,6 +12,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
+	"internal/testenv"
 	"testing"
 )
 
@@ -116,6 +117,8 @@ const _ = unsafe.Offsetof(struct{ x int64 }{}.x)
 
 // Issue #53884.
 func TestAtomicAlign(t *testing.T) {
+	testenv.MustHaveGoBuild(t) // The Go command is needed for the importer to determine the locations of stdlib .a files.
+
 	const src = `
 package main
 

src/go/types/typestring_test.go

@@ -125,6 +125,7 @@ var dependentTestTypes = []testEntry{
 }
 
 func TestTypeString(t *testing.T) {
+	// The Go command is needed for the importer to determine the locations of stdlib .a files.
 	testenv.MustHaveGoBuild(t)
 
 	var tests []testEntry