[res.on.exception.handling] Add cross-reference to [except.spec] (#7058)

Author: Eisenwave

source/lib-intro.tex

@@ -3844,7 +3844,7 @@
 Destructor operations defined in the \Cpp{} standard library
 shall not throw exceptions.
 Every destructor in the \Cpp{} standard library shall behave as if it had a
-non-throwing exception specification.
+non-throwing exception specification\iref{except.spec}.
 
 \pnum
 Functions defined in the