Now able build by MinGW. All warnings were fixed. (#584)

* fix wrong libusb extract command

* update libusb to 1.0.21 under windows

* fix few -Wformat warnings

* add usleep realisation for win32

* Get rid of unused defines in mimgw.h

* fix format warning for mingw

* Add prefix SEMIXOST_ to semihost defines.
Fix redefine warnings of mingw.