x/mobile: ios tag not added any more automatically

[karalabe]

I've tried to build a mobile package for ios, and was surprised to get strange compilation errors. It turned out that even though I specified --target=ios, the tags used during build was empty. After specifying explicitly --tags=ios too beside the target, compilation succeeded correctly. My guess is that some refactor broke this as I remember seeing commits in the code adding the ios tag.

[eliasnaur]

Can you provide with an example that breaks? Much has happened since this was reported and I believe the ios tag is passed in gomobile bind and gomobile build.