* Add MinGW and WinXP support, remove Win SDK dep when using MinGW
Was meant to add MinGW support only, WinXP support was made by accident.
Changes:
* Remove Win SDK dependency when compiled with MinGW
* Remap the Win SDK-depended functions to string.h substitutes
* Remap missing WinAPI call RegSetKeyValueW to a substitute function
* Remove warnings by pragma when using MinGW
