os: Add some exec.ProcessState stubs

Author: QuLogic

src/os/exec.go

@@ -34,6 +34,19 @@ func (p *ProcessState) Success() bool {
 	return false // TODO
 }
 
+// Sys returns system-dependent exit information about
+// the process. Convert it to the appropriate underlying
+// type, such as syscall.WaitStatus on Unix, to access its contents.
+func (p *ProcessState) Sys() interface{} {
+	return nil // TODO
+}
+
+// ExitCode returns the exit code of the exited process, or -1
+// if the process hasn't exited or was terminated by a signal.
+func (p *ProcessState) ExitCode() int {
+	return -1 // TODO
+}
+
 type Process struct {
 	Pid int
 }