set LINKER_LANGUAGE CXX for ref-cmake

[kungfooman]

Was running into this issue for linux build testing:

https://stackoverflow.com/questions/11801186/cmake-unable-to-determine-linker-language-with-c

[kungfooman]

Wow, I just realized that my compile problems on Linux and Windows stem from the fact that I didn't use npm init first.

Instead I just made a new directory and called npm install fastcall.

I don't know if you want to support the case of missing npm init, I guess it makes the build process a bit more resilient and won't hurt.