Fix a build issue on mingw
Fix a build issue on mingw

godbyk/OSVR-Core,godbyk/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core,OSVR/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core,OSVR/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core,godbyk/OSVR-Core,OSVR/OSVR-Core