Fix LLVM rtl compilation by disabling yield/pause inside TThread.SpinWait method

rtl/objpas/classes/classes.inc

@@ -909,7 +909,7 @@ begin
     as volatile, so the access won't be optimized away by the compiler. (KB) }
   for i:=1 to aIterations do
     begin
-    {$if FPC_FULLVERSION<30300}
+    {$if (FPC_FULLVERSION<30300) or defined(CPULLVM)}
     Inc(SpinWaitDummy); // SpinWaitDummy *MUST* be global
     {$else}
     {$IF defined(CPUX86_64) or Defined(CPUI386)}