UnicodeException.this() should be @nogc

src/core/exception.d

@@ -350,7 +350,7 @@ class UnicodeException : Exception
 {
     size_t idx;
 
-    this( string msg, size_t idx, string file = __FILE__, size_t line = __LINE__, Throwable next = null ) @safe pure nothrow
+    this( string msg, size_t idx, string file = __FILE__, size_t line = __LINE__, Throwable next = null ) @safe pure nothrow @nogc
     {
         super( msg, file, line, next );
         this.idx = idx;