migrate to upstream libcompose in one and a half go

vendor/github.com/opencontainers/runc/libcontainer/setgroups_linux.go

@@ -0,0 +1,11 @@
+// +build linux,go1.5
+
+package libcontainer
+
+import "syscall"
+
+// Set the GidMappingsEnableSetgroups member to true, so the process's
+// setgroups proc entry wont be set to 'deny' if GidMappings are set
+func enableSetgroups(sys *syscall.SysProcAttr) {
+	sys.GidMappingsEnableSetgroups = true
+}