Implemented NtYieldExecution.

diff --git a/include/winternl.h b/include/winternl.h
index 21b6428..5dc816e 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -1371,6 +1371,7 @@
 NTSTATUS  WINAPI NtWaitForMultipleObjects(ULONG,const HANDLE*,BOOLEAN,BOOLEAN,const LARGE_INTEGER*);
 NTSTATUS  WINAPI NtWriteFile(HANDLE,HANDLE,PIO_APC_ROUTINE,PVOID,PIO_STATUS_BLOCK,const void*,ULONG,PLARGE_INTEGER,PULONG);
 NTSTATUS  WINAPI NtWriteVirtualMemory(HANDLE,void*,const void*,SIZE_T,SIZE_T*);
+NTSTATUS  WINAPI NtYieldExecution(void);
 
 void      WINAPI RtlAcquirePebLock(void);
 BYTE      WINAPI RtlAcquireResourceExclusive(LPRTL_RWLOCK,BYTE);