cmd/link, go/internal/gccgoimporter: get ar from env by default in tests

Change-Id: Ib64b1f641fcf795a51aaf31639d37927dab519e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/622237
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: ChangWangMa

src/cmd/link/dwarf_test.go

@@ -121,10 +121,14 @@ func testDWARF(t *testing.T, buildmode string, expectDWARF bool, env ...string)
 
 			if buildmode == "c-archive" {
 				// Extract the archive and use the go.o object within.
-				cmd := testenv.Command(t, "ar", "-x", exe)
+				ar := os.Getenv("AR")
+				if ar == "" {
+					ar = "ar"
+				}
+				cmd := testenv.Command(t, ar, "-x", exe)
 				cmd.Dir = tmpDir
 				if out, err := cmd.CombinedOutput(); err != nil {
-					t.Fatalf("ar -x %s: %v\n%s", exe, err, out)
+					t.Fatalf("%s -x %s: %v\n%s", ar, exe, err, out)
 				}
 				exe = filepath.Join(tmpDir, "go.o")
 			}

src/go/internal/gccgoimporter/importer_test.go

@@ -180,11 +180,15 @@ func TestObjImporter(t *testing.T) {
 
 		runImporterTest(t, imp, initmap, &test)
 
-		cmd = testenv.Command(t, "ar", "cr", afile, ofile)
+		ar := os.Getenv("AR")
+		if ar == "" {
+			ar = "ar"
+		}
+		cmd = testenv.Command(t, ar, "cr", afile, ofile)
 		out, err = cmd.CombinedOutput()
 		if err != nil {
 			t.Logf("%s", out)
-			t.Fatalf("ar cr %s %s failed: %s", afile, ofile, err)
+			t.Fatalf("%s cr %s %s failed: %s", ar, afile, ofile, err)
 		}
 
 		runImporterTest(t, arimp, arinitmap, &test)