go/internal/gcimporter: skip typeparam import tests on unified builders

CL 351855 introduced a typeparam test that imported the constraints
package. As reported in golang/go#48595, this package is currently
breaking with the unified export data format.

Updates golang/go#48595

Change-Id: I1b77955c767a2e890d8d8829cca6455a4e79c5ee
Reviewed-on: https://go-review.googlesource.com/c/tools/+/352853
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

go/internal/gcimporter/iexport_go118_test.go

@@ -76,6 +76,10 @@ func TestImportTypeparamTests(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	if isUnifiedBuilder() {
+		t.Skip("unified export data format is currently unsupported")
+	}
+
 	for _, entry := range list {
 		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".go") {
 			// For now, only consider standalone go files.

go/internal/gcimporter/iexport_test.go

@@ -63,6 +63,12 @@ func iexport(fset *token.FileSet, pkg *types.Package) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
+// isUnifiedBuilder reports whether we are executing on a go builder that uses
+// unified export data.
+func isUnifiedBuilder() bool {
+	return os.Getenv("GO_BUILDER_NAME") == "linux-amd64-unified"
+}
+
 func TestIExportData_stdlib(t *testing.T) {
 	if runtime.Compiler == "gccgo" {
 		t.Skip("gccgo standard library is inaccessible")
@@ -88,7 +94,7 @@ func TestIExportData_stdlib(t *testing.T) {
 	// TryBots.
 	//
 	// TODO(#48595): fix this test with GOEXPERIMENT=unified.
-	isUnified := os.Getenv("GO_BUILDER_NAME") == "linux-amd64-unified"
+	isUnified := isUnifiedBuilder()
 	for _, path := range buildutil.AllPackages(conf.Build) {
 		if !(isUnified && testenv.UsesGenerics(path)) {
 			conf.Import(path)