[Bug c++/120498] error: either all initializer clauses should be designated or none of them should be when designated-initialising nested union members(?) (same code accepted as C)

[nabijaczleweli at nabijaczleweli dot xyz via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120498

--- Comment #10 from наб <nabijaczleweli at nabijaczleweli dot xyz> ---
Cool. Can you reach the same conclusion about the original unminified sample
which uses struct sigaction's sa_handler member directly?
  #include <signal.h>
  struct sigaction sa = {.sa_flags = SA_RESETHAND, .sa_handler = 0};

How do you decode and fix the error produced thusly?