[client] Drop SSH privileges through libc in PKCS#11 package builds (#8323)

client/ssh/server/setid_unix.go

@@ -0,0 +1,25 @@
+//go:build unix && !(pkcs11 && linux && !android && (amd64 || arm64))
+
+package server
+
+import "syscall"
+
+func setgroups(gids []int) error {
+	return syscall.Setgroups(gids)
+}
+
+func setgid(gid int) error {
+	return syscall.Setgid(gid)
+}
+
+func setuid(uid int) error {
+	return syscall.Setuid(uid)
+}
+
+func setegid(egid int) error {
+	return syscall.Setegid(egid)
+}
+
+func seteuid(euid int) error {
+	return syscall.Seteuid(euid)
+}