runtime: store start PC in pcvalueCache
Currently, pcvalue only returns a valid start PC if cache is nil.
We're about to eliminate the cache argument and always use a pcvalue
cache, so make sure the cache stores the start PC and always return it
from pcvalue.
Change-Id: Ie8854af4b7e7ba1c2a17a495d9229320821daa23
Reviewed-on: https://go-review.googlesource.com/c/go/+/515275
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>