cmd/compile/internal: small tweak to merge locals trace output
For -gcflags=-d=mergelocalstrace=1 (which reports estimated savings
from stack slot merging), emit separate values for pointerful vs
non-pointerful variables, for a bit more detail.
Updates #62737.
Updates #65532.
Updates #65495.
Change-Id: I9dd27d2a254036448c85c13d189d1ed36157c9d7
Reviewed-on: https://go-review.googlesource.com/c/go/+/576680
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>