Revert "runtime: drop stack-allocated pcvalueCaches"

Revert "runtime: drop stack-allocated pcvalueCaches"

This reverts CL 515277

Change-Id: Ie10378eed4993cb69f4a9b43a38af32b9d743155
Reviewed-on: https://go-review.googlesource.com/c/go/+/516855
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>