fix a static build

[ahorek]

on Windows, LIBWINPTHREAD-1.DLL is still linked dynamically

a static build shouldn't depend on external libraries. Especially JRuby should be able to load the static library at runtime without a devkit environment. However, devkit tools are still necessary to build the library on JRuby. see #182 (comment)

[mohits]

Thanks for fixing this! I guess this will be deployed in the next gem release? For now, I can see that if I add c:\Ruby26-x64\msys64\mingw64\bin it is able to find LIBWINPTHREAD-1.DLL and related dependencies to be able to load sassc from JRuby. I have this note added to my post about building and installing sassc within JRuby, and will update it once it works without this workaround :)

[enebo]

Any chance we can get this in a release? Having to have a C tool chain on windows for JRuby to install one gem is pretty inconvenient.