[Bug libstdc++/69721] [6 Regression] math.h is broken, unqualified use of __is_integer

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69721

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Definitely invalid. It might have worked before because <math.h> only declared
extern "C" functions, which don't include namespaces in their mangled names,
but the code always had undefined behaviour.

Now that <math.h> is implemented by including <cmath> (which defines extern
"C++" functions where namespaces matter) the undefined code stops working.
That's the problem with undefined code that just happens to work today, it
might stop working at any time.