[release-branch.go1.12] syscall: skip TestSyscallNoError when temp dir is mounted nosuid

Fixes #30258

Change-Id: I73b63eb9d3aca00f562fdc3af010e96269bb6b9c
Reviewed-on: https://go-review.googlesource.com/c/162891
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
(cherry picked from commit 5fcc2407)
Reviewed-on: https://go-review.googlesource.com/c/162818Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/syscall/syscall_linux_test.go

@@ -360,10 +360,23 @@ func TestSyscallNoError(t *testing.T) {
 		strconv.FormatUint(uint64(-uid), 10) + " / " +
 		strconv.FormatUint(uint64(uid), 10)
 	if got != want {
+		if filesystemIsNoSUID(tmpBinary) {
+			t.Skip("skipping test when temp dir is mounted nosuid")
+		}
 		t.Errorf("expected %s, got %s", want, got)
 	}
 }
 
+// filesystemIsNoSUID reports whether the filesystem for the given
+// path is mounted nosuid.
+func filesystemIsNoSUID(path string) bool {
+	var st syscall.Statfs_t
+	if syscall.Statfs(path, &st) != nil {
+		return false
+	}
+	return st.Flags&syscall.MS_NOSUID != 0
+}
+
 func syscallNoError() {
 	// Test that the return value from SYS_GETEUID32 (which cannot fail)
 	// doesn't get treated as an error (see https://golang.org/issue/22924)