feat: Catch up 4.13.1 minor fixes and performance improvements

Signed-off-by: Jim.Idle <jimi@idle.ws>

runtime/Go/antlr/v4/mutex.go

@@ -0,0 +1,38 @@
+// +build !nomutex
+
+package antlr
+
+import "sync"
+
+type Mutex struct {
+	mu sync.Mutex
+}
+
+func (m *Mutex) Lock() {
+	m.mu.Lock()
+}
+
+func (m *Mutex) Unlock() {
+	m.mu.Unlock()
+}
+
+
+type RWMutex struct {
+	mu sync.RWMutex
+}
+
+func (m *RWMutex) Lock() {
+	m.mu.Lock()
+}
+
+func (m *RWMutex) Unlock() {
+	m.mu.Unlock()
+}
+
+func (m *RWMutex) RLock() {
+	m.mu.RLock()
+}
+
+func (m *RWMutex) RUnlock() {
+	m.mu.RUnlock()
+}

runtime/Go/antlr/v4/mutex_nomutex.go

@@ -0,0 +1,31 @@
+// +build nomutex
+
+package antlr
+
+type Mutex struct{}
+
+func (m *Mutex) Lock() {
+	// No-op
+}
+
+func (m *Mutex) Unlock() {
+	// No-op
+}
+
+type RWMutex struct{}
+
+func (m *RWMutex) Lock() {
+	// No-op
+}
+
+func (m *RWMutex) Unlock() {
+	// No-op
+}
+
+func (m *RWMutex) RLock() {
+	// No-op
+}
+
+func (m *RWMutex) RUnlock() {
+	// No-op
+}