runtime: enable precise GC checks when using stack maps

In the runtime there are bad pointer checks that currently don't
work with the concervative collector. With stack maps, the GC is
precise and the checks should work. Enable them.

Change-Id: Ic0ff2c6065bc116a9f4c33e115eae89fda98b160
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/153871
Reviewed-by: Ian Lance Taylor <iant@golang.org>
3 files changed