Vendor Teakra, make emulator own DSP RAM and add DSP RAM to fastmem (#806)

* DSP: Own DSP RAM and add it to fastmem

* Vendor Teakra

* Add MacOS support to fastmem

* Fix MacOS fastmem paths

* Fix iOS build

third_party/teakra/src/bit.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <limits>
+#include <type_traits>
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+namespace std20 {
+
+// A simple (and not very correct) implementation of C++20's std::log2p1
+template <class T>
+constexpr T log2p1(T x) noexcept {
+    static_assert(std::is_integral_v<T> && std::is_unsigned_v<T>);
+    if (x == 0)
+        return 0;
+#ifdef _MSC_VER
+    unsigned long index = 0;
+    _BitScanReverse64(&index, x);
+    return static_cast<T>(index) + 1;
+#else
+    return static_cast<T>(std::numeric_limits<unsigned long long>::digits - __builtin_clzll(x));
+#endif
+}
+
+} // namespace std20