[Bug libstdc++/82644] Non-standard hypergeometric special functions defined in strict modes

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82644

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
While I'm on the subject, we fail to import the special functions into the
global namespace in <math.h> (because the wrong macro is checked):

#include <math.h>
namespace test {
  using std::beta; // OK
  using ::beta;    // ERROR
}

specfun.cc:4:11: error: ‘::beta’ has not been declared
   using ::beta;    // ERROR
           ^~~~

And we don't properly document IS 29124 support, and implementation-defined
behaviour.