crypto: make CRYPTO_DEFINE_HASH_FUNCTIONS adhere strict aliasing

This code could've caused issues if the pointer to the `public_key`, `key_image`, `hash`, etc wasn't aligned on an 8-byte boundary.

src/crypto/generic-ops.h

@@ -60,14 +60,18 @@ namespace crypto { \
 namespace crypto { \
   static_assert(sizeof(std::size_t) <= sizeof(type), "Size of " #type " must be at least that of size_t"); \
   inline std::size_t hash_value(const type &_v) { \
-    return reinterpret_cast<const std::size_t &>(_v); \
+    std::size_t h; \
+    memcpy(&h, &_v, sizeof(h)); \
+    return h; \
   } \
 } \
 namespace std { \
   template<> \
   struct hash<crypto::type> { \
     std::size_t operator()(const crypto::type &_v) const { \
-      return reinterpret_cast<const std::size_t &>(_v); \
+      std::size_t h; \
+      memcpy(&h, &_v, sizeof(h)); \
+      return h; \
     } \
   }; \
 }