Bindings are independent of any particular GOOS/GOARCH pair and
as such the gomobile bind command doesn't set GOOS nor GOARCH when
running gobind. However, the ios tag was still added to the list
of tags to pass to gobind for -target=ios.
Move the ios tag to when actually building the bound packages,
mirroring gomobile build.
Add TestBindIOS and update TestBindAndroid.
Updates golang/go#24644
Change-Id: I007829c26036427a3376bba11a1ccb86e7338848
Reviewed-on: https://go-review.googlesource.com/104458
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
90139f6bae