compiler: add break label in 1,2-case select statement lowering

CL 184998 added optimizations for one- and two-case select
statements. But it didn't handle break statement in the select
case correctly. Specifically, it didn't add the label definition,
so it could result in a dangling goto. This CL fixes this, by
adding the label definition.

A test case is CL 185520.

Change-Id: I98d30f599f1c4c71b91724ac394b8761d1b70b7d
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/185519
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed