MAME doesn't build with Clang 20.1.0 on Windows

[Osso13]

Yesterday pacman started distributing Clang 20.1.0. MAME fails to build. This will be a problem when the CI starts pulling that Clang version. There are problems both in 3rdparty and in MAME proper. This is an example of the latter:

../../../../../src/devices/cpu/alto2/a2disp.cpp:502:9: error: first argument in call to 'memset' is a pointer to
non-trivially copyable type 'struct (unnamed struct at ../../../../../src/devices/cpu/alto2/a2disp.h:195:1)'
[-Werror,-Wnontrivial-memcall]
502 | memset(&m_dsp, 0, sizeof(m_dsp));
| ^
../../../../../src/devices/cpu/alto2/a2disp.cpp:502:9: note: explicitly cast the pointer to silence this warning
502 | memset(&m_dsp, 0, sizeof(m_dsp));
| ^
| (void*)
../../../../../src/devices/cpu/alto2/a2ether.cpp:1310:9: error: first argument in call to 'memset' is a pointer to
non-trivially copyable type 'struct (unnamed struct at ../../../../../src/devices/cpu/alto2/a2ether.h:50:1)'
[-Werror,-Wnontrivial-memcall]
1310 | memset(&m_eth, 0, sizeof(m_eth));
| ^
../../../../../src/devices/cpu/alto2/a2ether.cpp:1310:9: note: explicitly cast the pointer to silence this warning
1310 | memset(&m_eth, 0, sizeof(m_eth));
| ^
| (void*)

[Osso13]

ocornut/imgui@419a9ad
This seems to address the errors in 3rdparty