x/mobile: reduce size of generated artifacts

[ToJen]

The size of Go builds can be shrunk with the ldflags build option like this:
go build -ldflags '-s -w' -o my_app.exe

This can be reduced further with UPX as such:
upx -o my_app_min.exe my_app.exe

More on this here.

I'm able to pass the ldflags into gomobile like this:
gomobile bind -ldflags '-s -w' -target=android github.com/my/app.

I would like to "inject" UPX somewhere in the bind process to reduce the size of my generated .aar and .framework.

A possible flow is this:

1. Build: go build -ldflags '-s -w' -o my_app.exe
2. Shrink: upx -o my_app_min.exe my_app.exe
3. Pass into gomobile:gomobile bind --from-build=my_app_min.exe -target=android github.com/my/app

[toothrot]

/cc @hyangah

[ToJen]

@toothrot @hyangah what's a place to start the investigation. I believe many users will benefit from a smaller aar and framework. Would it make sense at all to achieve it this way?

[ToJen]

i believe it will be somewhere here:
android: https://github.com/golang/mobile/blob/master/cmd/gomobile/bind_androidapp.go#L52
ios: https://github.com/golang/mobile/blob/master/cmd/gomobile/bind_iosapp.go#L38