Fixing the build on Linux(Ubuntu).

This was the work i put to make CppSharp compile on Ubuntu 14.04.1, mingw version 4.8.2 , mono version 3.10.0 , the purpose of the pull request is to help the maintainers, this pull request will show them how much work is needed to make it able to build on Linux. I have not verified that  build on other platforms is not broken after these changes except for Linux but it should not be.
can not compare unspecified pointer to pointer to integer. may be a cast would have been better, ? not sure