You are basically following the instructions from litecoin
However you may have trouble unless you have run this command:
PATH=$(echo "$PATH" | sed -e 's/:\/mnt.*//g') # strip out problematic Windows %PATH% imported var
... slightly before you run this command make HOST=x86_64-w64-mingw32
(kind of as per @ https://github.com/bitcoin/bitcoin/blob/0.15/doc/build-windows.md)
Ridiculously enough, you may need to manually (as a human) click the "OK" button on your PC when a "conftest.exe - System Error" box appears in the middle of your compiling (while it's on the "clock_gettime_monotonic") step. No biggie, just do it!