ntoskrnl.exe: Implement ExAcquireFastMutex and ExReleaseFastMutex.

dlls/ntoskrnl.exe/ntoskrnl.exe.spec

+@ stdcall -arch=arm,arm64,x86_64 ExAcquireFastMutex(ptr)
 @ stdcall -fastcall ExAcquireFastMutexUnsafe(ptr)
 @ stub ExAcquireRundownProtection
 @ stub ExAcquireRundownProtectionEx
@@ -8,6 +9,7 @@
 @ stdcall -fastcall -arch=i386 ExInterlockedPopEntrySList(ptr ptr) NTOSKRNL_ExInterlockedPopEntrySList
 @ stdcall -fastcall -arch=i386 ExInterlockedPushEntrySList (ptr ptr ptr) NTOSKRNL_ExInterlockedPushEntrySList
 @ stub ExReInitializeRundownProtection
+@ stdcall -arch=arm,arm64,x86_64 ExReleaseFastMutex(ptr)
 @ stdcall -fastcall ExReleaseFastMutexUnsafe(ptr)
 @ stdcall -fastcall ExReleaseResourceLite(ptr)
 @ stub ExReleaseRundownProtection

dlls/ntoskrnl.exe/sync.c

@@ -732,6 +732,28 @@ void FASTCALL ExReleaseFastMutexUnsafe( FAST_MUTEX *mutex )
         KeSetEvent( &mutex->Event, IO_NO_INCREMENT, FALSE );
 }
 
+#ifndef __i386__
+
+/***********************************************************************
+ *           ExAcquireFastMutex    (NTOSKRNL.@)
+ */
+void WINAPI ExAcquireFastMutex( FAST_MUTEX *mutex )
+{
+    /* FIXME: lower IRQL */
+    ExAcquireFastMutexUnsafe( mutex );
+}
+
+/***********************************************************************
+ *           ExReleaseFastMutex    (NTOSKRNL.@)
+ */
+void WINAPI ExReleaseFastMutex( FAST_MUTEX *mutex )
+{
+    ExReleaseFastMutexUnsafe( mutex );
+    /* FIXME: restore IRQL */
+}
+
+#endif /* __i386__ */
+
 /* Use of the fields of an ERESOURCE structure seems to vary wildly between
  * Windows versions. The below implementation uses them as follows:
  *