clang on Windows: unused typedef warning for VerifySizesAreEqual (used for static assertion) about double-conversion HOT 4 CLOSED

../../third_party/icu/source/i18n/double-conversion-utils.h(342,20):  error: unused typedef 'VerifySizesAreEqual' [-Werror,-Wunused-local-typedef]
      typedef char VerifySizesAreEqual[sizeof(Dest) == sizeof(Source) ? 1 : -1];

#if __cplusplus >= 201103L
#define DOUBLE_CONVERSION_STATIC_ASSERT(expr, msg) static_assert(expr, #msg)
#else
namespace double_conversion {
template <bool> struct CompileAssert {};
}

typedef double_conversion::CompileAssert<static_cast<bool>(expr)> StaticAssert[bool(expr) ? 1 : -1]; \
(void)msg
#endif

DOUBLE_CONVERSION_STATIC_ASSERT(sizeof(Dest) == sizeof(Source));

 #else
 #error Target architecture was not detected as supported by Double-Conversion.
 #endif
 
-#if defined(__GNUC__)
-#define DOUBLE_CONVERSION_UNUSED __attribute__((unused))
-#else
-#define DOUBLE_CONVERSION_UNUSED
-#endif
-
 #if defined(_WIN32) && !defined(__MINGW32__)
 
 typedef signed char int8_t;
@@ -336,8 +332,12 @@ template <class Dest, class Source>
 inline Dest BitCast(const Source& source) {
   // Compile time assertion: sizeof(Dest) == sizeof(Source)
   // A compile error here means your Dest and Source have different sizes.
-  DOUBLE_CONVERSION_UNUSED
-      typedef char VerifySizesAreEqual[sizeof(Dest) == sizeof(Source) ? 1 : -1];
+#if __cplusplus >= 201103L
+  static_assert(sizeof(Dest) == sizeof(Source),
+                "source and destination size mismatch");
+#else
+  typedef char StaticAssert[sizeof(Dest) == sizeof(Source) ? 1 : -1];
+#endif
 
   Dest dest;
   memmove(&dest, &source, sizeof(dest));