FHU: Add a non-block thread local ringbuffer

I keep rewriting this thing when I want to see some history on
something. Throw it in a FHU utility so I can stop wasting my time.

FEXHeaderUtils/FEXHeaderUtils/RingBuffer.h

@@ -0,0 +1,21 @@
+#pragma once
+#include <bit>
+#include <cstddef>
+
+namespace FHU {
+// This is a fast thread-local non-blocking ring-buffer.
+// Very useful for debugging purposes to see the history of something.
+template<typename T, size_t Elements>
+requires (std::has_single_bit(Elements) && std::is_trivially_copyable_v<T>)
+class [[deprecated("Not for production use")]] NonBlockRingBuffer final {
+public:
+  void emplace(T Val) {
+    Ring[Current] = Val;
+    Current = (Current + 1) & (Elements - 1);
+  }
+
+private:
+  T Ring[Elements] {};
+  size_t Current {};
+};
+} // namespace FHU