Use <version> instead of the deprecated <ciso646>.

<ciso646> only ever provided the C++98 alternative-token macros (and, or, not),
which are keywords on every compiler MIOpen supports. Since C++20 it is no
longer a standard header, and GCC 16's libstdc++ says so with a #warning --
which MIOpen's own -Werror turns into a hard build failure:

  /usr/lib/gcc/.../g++-v16/ciso646:49:6: error: "<ciso646> is not a standard
  header since C++20, use <version> to detect implementation-specific macros"
  [-Werror,-W#warnings]

<version> is what the warning recommends and what the include was actually
being used for here (implementation macros). Only one file in the tree includes
it. verified 2026-08-30.
--- a/src/include/miopen/serializable.hpp
+++ b/src/include/miopen/serializable.hpp
@@ -27,7 +27,7 @@
 #ifndef GUARD_MLOPEN_SERIALIZABLE_HPP
 #define GUARD_MLOPEN_SERIALIZABLE_HPP
 
-#include <ciso646>
+#include <version>
 #include <miopen/config.h>
 #include <iostream>
 #include <sstream>