Fix the build and timezone offset with MinGW (#4449)
Fix the build and timezone offset with MinGW (#4449)

Changes:
- Use _WIN32 macro instead of _WINDOWS
- Fix build error - "no previous declaration for 'UnixTimeToFileTime'"
- Fix conversion build errors
- Remove useless _tzset() call
- Use GetSystemTimeAsFileTime() on Windows to get current time
- Unify and simplify time conversion Windows helper functions

Fixes #4240

JerryScript-DCO-1.0-Signed-off-by: Csaba Osztrogonác csaba.osztrogonac@h-lab.eu
dbatyai/jerryscript,zherczeg/jerryscript,jerryscript-project/jerryscript,zherczeg/jerryscript,bzsolt/jerryscript,jerryscript-project/jerryscript,dbatyai/jerryscript,dbatyai/jerryscript,robertsipka/jerryscript,bzsolt/jerryscript,jerryscript-project/jerryscript,jerryscript-project/jerryscript,zherczeg/jerryscript,zherczeg/jerryscript,zherczeg/jerryscript,robertsipka/jerryscript,bzsolt/jerryscript,bzsolt/jerryscript,jerryscript-project/jerryscript,bzsolt/jerryscript,robertsipka/jerryscript,dbatyai/jerryscript,robertsipka/jerryscript,robertsipka/jerryscript,dbatyai/jerryscript,robertsipka/jerryscript