Strict iterators can't be used on Windows, they lead to a link error
when application code iterates over a QVector<QPoint> for instance, unless
Qt itself was also built with strict iterators.
See example at https://bugreports.qt.io/browse/AUTOSUITE-946
Technically this would be fine for mingw, but not for MSVC neither
clang-cl (which also uses the MSVC ABI). I think it's fine to just
disable it for all Windows compilers, since any iterators misuse
will be detected on Unix anyway.