runtime compiles on Windows

Signed-off-by: John Howard <jhoward@microsoft.com>

runtime/runtime_windows.go

@@ -0,0 +1,10 @@
+package runtime
+
+// Checkpoint is not supported on Windows.
+// TODO Windows: Can eventually be factored out entirely.
+type Checkpoint struct {
+}
+
+// PlatformProcessState container platform-specific fields in the ProcessState structure
+type PlatformProcessState struct {
+}