building windows on arm

[sadan4]

when build on windows on arm, it grabs the x64 build unconditionally when it should grab win-arm64

https://github.com/infinyon/node-bindgen/blob/02dcd71418d09867262335feaa5b25d18835aeaa/nj-build/src/lib.rs#L80-L84

this gives a linker error when trying to build