_variant_t inherits from tagVARIANT aka VARIANT and C++ will always prioritize the built-in conversion to the base class over the use of a user-defined conversion operator.
Fixes GCC 13 warning:
In file included from C:/ReactOS/reactos/sdk/include/vcruntime/comdef.h:19,
from C:/ReactOS/reactos/sdk/lib/comsupp/comsupp.cpp:16:
C:/ReactOS/reactos/sdk/include/vcruntime/comutil.h:423:3: error: converting '_variant_t' to a base class 'VARIANT' {aka 'tagVARIANT'} will never use a type conversion operator [-Werror=class-conversion]
423 | operator VARIANT() const throw();
| ^~~~~~~~
These headers come with the MS compiler. Some of them are standard, like emmintrin.h, others are MS specific like crtdefs.h
This separation will allow using MS CRT headers. Eventually it can allow compiling with the compilers' runtime headers.
