compiler: detect failure to set init priority for package

This would have caught the problem fixed by https://golang.org/cl/43610.

Change-Id: I357f6618cbe8c034f64512bbb83bb740f0149c2f
Reviewed-on: https://go-review.googlesource.com/43999
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed