Support for Mingw64 compiler

This patch set adds support for the compilation of Lunchbox with MinGW64.

The changes were tested with commit acb7920fbc151cf32e664325a442134af142332b as a branch base using MinGW64 runtime 3.2 on Linux. The library files were created without issues and the tests linked properly against the library.
really needed? Is it not enough to only export the necessary functions?