node-pre-gyp doesn't handle arm architectures properly.

Nobody has claimed this yet.

The "arm" target in itself isn't enough. If you look at [node binary distributions](https://nodejs.org/dist/v8.9.4/), you have 3 variants for arm: `armv6l`, `armv7l`, and `arm64`.

An example of an `armv6l` platform is a raspberry pi zero. Installing nodejs on a raspberry pi zero through nvm will yield the correct download of the correct binary (armv6l).

An example of an `armv7l` platform is a raspberry pi 3. Installing nodejs on a raspberry pi 3 through nvm will also yield the correct download of the correct binary (armv7l).

However, for both platforms, node-pre-gyp identify them as "arm", meaning we can only cross compile and publish a single version of node-pre-gyp packages, either armv6l or armv7l, which aren't interchangeable due to dynamic library versions and tags.

This creates a problem where users will be able to download the wrong version of the package for their platform, and crash on load. The only method for them to fix it is to uninstall the node-pre-gyp enabled package, and re-install it using a flag to force falling back on ignoring published packages and compile from source instead, which is not obvious.

Also, the documentation states that the only correct values for --target_arch are ia32, x64 and arm, whereas arm64 is in fact a valid keyword to use here. The produced packages work properly on an arm64 environment.

Start by tracing how node-pre-gyp identifies target architectures and how the --target_arch documentation lists supported values. Verify that armv6l, armv7l, and arm64 select distinct compatible packages, and that the documentation reflects the valid arm64 keyword.

Written by the indexing model from the issue text.