add JSONCPP_NORETURN where appropriate

Found with clang's -Wmissing-noreturn

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Author: neheb

include/json/value.h

@@ -879,7 +879,7 @@ class JSON_API ValueIterator : public ValueIteratorBase {
   using SelfType = ValueIterator;
 
   ValueIterator();
-  JSONCPP_OP_EXPLICIT ValueIterator(const ValueConstIterator& other);
+  JSONCPP_NORETURN JSONCPP_OP_EXPLICIT ValueIterator(const ValueConstIterator& other);
   ValueIterator(const ValueIterator& other);
 
 private: