Switch to golang/dep.

vendor/github.com/opencontainers/runc/libcontainer/compat_1.5_linux.go

@@ -0,0 +1,10 @@
+// +build linux,!go1.5
+
+package libcontainer
+
+import "syscall"
+
+// GidMappingsEnableSetgroups was added in Go 1.5, so do nothing when building
+// with earlier versions
+func enableSetgroups(sys *syscall.SysProcAttr) {
+}