Implement getTimezoneOffset for Win32

[afulsamet]

Useful links

• GetTimeZoneInformation
• GetTimeZoneInformation#Remarks

Notes

The bias is the difference, in minutes, between UTC time and local time.

[chqrlie]

Hello! The checks for windows-mingw targets failed because <windows.h> and friends are only included if _MSC_VER is defined whereas the patch depends on _WIN32 being defined.

I am not fully familiar with the mingw system, I guess the windows headers should be included if _WIN32 is defined, not just for the Microsoft compiler.

[afulsamet]

Hello! The checks for windows-mingw targets failed because <windows.h> and friends are only included if _MSC_VER is defined whereas the patch depends on _WIN32 being defined.

I am not fully familiar with the mingw system, I guess the windows headers should be included if _WIN32 is defined, not just for the Microsoft compiler.

I tested new commit with GCC 13.2.0 (MinGW) and Clang 17.0.6 (MSVC), it works now.

[saghul]

Thank you!