Use arch instead of target_arch

[gergof]

When building for a different architecture using node-gyp, the arch option should be used. Using target_arch populates the variable usable in the binding.gyp file, but node-gyp will still do a build with the system's architecture.

[lovell]

Thanks for the PR. There's some logic in node-gyp that suggests target_arch is the expected name.

https://github.com/nodejs/node-gyp/blob/b3d41aeb737ddd54cc292f363abc561dcc0a614e/lib/build.js#L59

There's also a known bug in node-gyp relating to this - see nodejs/node-gyp#2865 - if that bug was fixed, would this change still be necessary?

[gergof]

I think it still would be necessary.
The target_arch variable is overwritten here: https://github.com/nodejs/node-gyp/blob/b3d41aeb737ddd54cc292f363abc561dcc0a614e/lib/create-config-gypi.js#L69

The documentation is also suggesting using --arch: https://github.com/nodejs/node-gyp/tree/b3d41aeb737ddd54cc292f363abc561dcc0a614e#command-options

This was probably not the case before, but since updating prebuild to version 12, even though target_arch is set to x64, the flags passed to the compiler state that the build arch should be arm64. With this change it works as expected without any side effects.

[vweevers]

See also prebuild/prebuildify#53 and prebuild/prebuildify#52 (comment)

[lovell]

Please can you update the failing "gyp is invoked with correct arguments" tests.

[gergof]

I've made the changes, the tests are passing now.

[lovell]

Thank you, LGTM