Added a spinlock template as well as a thread work pool class.

Also, optimized shader compilation to happen on threads.

core/bind/core_bind.cpp

@@ -2612,7 +2612,7 @@ void _Semaphore::_bind_methods() {
 
 _Semaphore::_Semaphore() {
 
-	semaphore = Semaphore::create();
+	semaphore = SemaphoreOld::create();
 }
 
 _Semaphore::~_Semaphore() {

core/bind/core_bind.h

@@ -642,7 +642,7 @@ public:
 class _Semaphore : public Reference {
 
 	GDCLASS(_Semaphore, Reference);
-	Semaphore *semaphore;
+	SemaphoreOld *semaphore;
 
 	static void _bind_methods();