Switch to Video_BeginField; hopefully fix or reduce some video stability problems by using Events.

git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@3740 8ced0084-cf51-0410-be5f-012b33b47a6e

Source/Core/Common/Src/Thread.h

@@ -71,6 +71,18 @@
 
 namespace Common
 {
+
+// MemFence: Neither the compiler nor the CPU can reorder memory accesses
+// beyond this barrier.
+__forceinline void MemFence()
+{
+#ifdef _WIN32
+	MemoryBarrier();
+#else
+	// TODO: UNIX experts, please implement the memory fence.
+#endif
+}
+
 class CriticalSection
 {
 #ifdef _WIN32