Compilation error on Windows and several timezone issues

Encountered compilation error while building agent on Windows:

'timezone' undeclared identifier in src/libs/zbxsysinfo/common/system.c

The problem is in these lines of system.c:

#if defined(HAVE_TM_TM_GMTOFF)
		gmtoff = tm->tm_gmtoff;
#else
		gmtoff = -timezone;
#endif

According to https://msdn.microsoft.com/en-us/library/ms235451%28v=vs.140%29.aspx and adjacent links, Microsoft abandoned standard in this aspect in favour of their own _underscored functions and global variables. I guess rewriting given piece of code in the following manner

#if defined(HAVE_TM_TM_GMTOFF)
		gmtoff = tm->tm_gmtoff;
#else
#ifdef _WINDOWS
		gmtoff = -_timezone;
#else
		gmtoff = -timezone;
#endif
#endif

should fix the issue. Or we can go even further and use "safer" functional equivalents".