use math defines on Mingw
do not use gcc-ar for MinGW 4.9
Merge branch 'mingw-support' of https://github.com/alex85k/Project-OSRM into alex85k-mingw-support
Merge branch 'alex85k-mingw-support' into develop
Merge branch 'develop' of github.com:Project-OSRM/osrm-backend into develop
prevent double compile of dependent compile units