cmd/go: avoid use of git -C, which does not exist in RHEL 7

Tested manually with "go test -run TestGetSubmodules".

Fixes #14194.

Change-Id: I4f563b2b8a38f3040d7631f74a7908ab65e0860b
Reviewed-on: https://go-review.googlesource.com/19154Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/vcs.go

@@ -122,7 +122,7 @@ var vcsGit = &vcsCmd{
 	name: "Git",
 	cmd:  "git",
 
-	createCmd:   []string{"clone {repo} {dir}", "-C {dir} submodule update --init --recursive"},
+	createCmd:   []string{"clone {repo} {dir}", "-go-internal-cd {dir} submodule update --init --recursive"},
 	downloadCmd: []string{"pull --ff-only", "submodule update --init --recursive"},
 
 	tagCmd: []tagCmd{
@@ -335,6 +335,15 @@ func (v *vcsCmd) run1(dir string, cmdline string, keyval []string, verbose bool)
 		args[i] = expand(m, arg)
 	}
 
+	if len(args) >= 2 && args[0] == "-go-internal-cd" {
+		if filepath.IsAbs(args[1]) {
+			dir = args[1]
+		} else {
+			dir = filepath.Join(dir, args[1])
+		}
+		args = args[2:]
+	}
+
 	_, err := exec.LookPath(v.cmd)
 	if err != nil {
 		fmt.Fprintf(os.Stderr,