bit_field: Re-enable code on MSVC

src/common/bit_field.h

@@ -125,21 +125,10 @@ public:
     // so that we can use this within unions
     BitField() = default;
 
-#ifndef _WIN32
     // We explicitly delete the copy assigment operator here, because the
     // default copy assignment would copy the full storage value, rather than
     // just the bits relevant to this particular bit field.
-    // Ideally, we would just implement the copy assignment to copy only the
-    // relevant bits, but this requires compiler support for unrestricted
-    // unions.
-    // MSVC 2013 has no support for this, hence we disable this code on
-    // Windows (so that the default copy assignment operator will be used).
-    // For any C++11 conformant compiler we delete the operator to make sure
-    // we never use this inappropriate operator to begin with.
-    // TODO: Implement this operator properly once all target compilers
-    // support unrestricted unions.
     BitField& operator=(const BitField&) = delete;
-#endif
 
     FORCE_INLINE BitField& operator=(T val)
     {