This patch to the Go frontend detects a failure to set the init
priority for a package.  This would have caught the bug fixed in the
patch in https://golang.org/cl/43610 aka
https://gcc.gnu.org/ml/gcc-patches/2017-05/msg01416.html .
Bootstrapped and ran Go tests on x86_64-pc-linux-gnu.  Committed to
mainline.

Ian