Windows compatibilty patches (rebased to develop)

copy of https://github.com/DennisOSRM/Project-OSRM/pull/979
with `develop` as  base branch.

No problem, I'll add the following code:
```c++
// Necessary workaround for Windows as VS doesn't implement C99
#ifdef _MSC_VER
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#define constexpr const static
#endif
```