* rename to emitPcln because I'd like to skip not only container types,
  but also something like "go.buildid" in the future.
* return bool instead of int.

Change-Id: I029adb81292f7dd2fe98e69f3877c5c27f32ec30
Reviewed-on: https://go-review.googlesource.com/59415Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>