ac_cxx_dynamic_cast

If the compiler supports dynamic_cast<>, define HAVE_DYNAMIC_CAST.

AC_DEFUN([AC_CXX_DYNAMIC_CAST],
[AC_CACHE_CHECK(whether the compiler supports dynamic_cast<>,
ac_cv_cxx_dynamic_cast,
[AC_LANG_SAVE
 AC_LANG_CPLUSPLUS
 AC_TRY_COMPILE([#include <typeinfo>
class Base { public : Base () {} virtual void f () = 0;};
class Derived : public Base { public : Derived () {} virtual void f () {} };],[
Derived d; Base& b=d; return dynamic_cast<Derived*>(&b) ? 0 : 1;],
 ac_cv_cxx_dynamic_cast=yes, ac_cv_cxx_dynamic_cast=no)
 AC_LANG_RESTORE
])
if test "$ac_cv_cxx_dynamic_cast" = yes; then
  AC_DEFINE(HAVE_DYNAMIC_CAST,,[define if the compiler supports dynamic_cast<>])
fi
])