This macro, if defined, is supposed to provide an alternative definition of the union any type. It was added in commit 0f4eea8fa1779e0 (June 1998) to let win32.h override union any with its own definition. That override was removed from win32.h in commit c06b86730d867c (July 1999).
For the past 25 years, this feature has been sitting there undocumented and unused.
This macro, if defined, is supposed to provide an alternative definition of the
union anytype. It was added in commit 0f4eea8fa1779e0 (June 1998) to let win32.h overrideunion anywith its own definition. That override was removed from win32.h in commit c06b86730d867c (July 1999).For the past 25 years, this feature has been sitting there undocumented and unused.