cmd/nm: don't rely on an erroneous install target in tests

Non-main packages in module mode should not be installed to
GOPATH/pkg, but due to golang#37015 they were installed there anyway.
This change switches the 'go install' command in testGoLib to instead
use 'go build -buildmode=archive' with an explicit output file.

For golang#37015.

Change-Id: I15781aa33d1b2adc6a4437a58622276f4e20b889
Reviewed-on: https://go-review.googlesource.com/c/go/+/416955
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>

Author: Bryan C. Mills

src/cmd/nm/nm_test.go

@@ -250,23 +250,14 @@ func testGoLib(t *testing.T, iscgo bool) {
 		t.Fatal(err)
 	}
 
-	args := []string{"install", "mylib"}
-	cmd := exec.Command(testenv.GoToolPath(t), args...)
+	cmd := exec.Command(testenv.GoToolPath(t), "build", "-buildmode=archive", "-o", "mylib.a", ".")
 	cmd.Dir = libpath
 	cmd.Env = append(os.Environ(), "GOPATH="+gopath)
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("building test lib failed: %s %s", err, out)
 	}
-	pat := filepath.Join(gopath, "pkg", "*", "mylib.a")
-	ms, err := filepath.Glob(pat)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(ms) == 0 {
-		t.Fatalf("cannot found paths for pattern %s", pat)
-	}
-	mylib := ms[0]
+	mylib := filepath.Join(libpath, "mylib.a")
 
 	out, err = exec.Command(testnmpath, mylib).CombinedOutput()
 	if err != nil {