Fix appveyor windows build (#420) * Fix msvcc dll build by adding dllexport decorations to all API declarations * Fix appveyor build for VS 2013 Use the new -DFFI_BUILDING_DLL for producing a working DLL. Update the msvcc.sh wrapper script to successfully compile the testsuite files. * MSVC build: suppress warnings in testsuite * fix testsuite on appveyor