cmd/compile: move FuncPC intrinsic handling to common helper
CL 539699 will need to do the equivalent of
internal/abi.FuncPCABIInternal to get the PC of a function value for the
runtime devirtualization check.
Move the FuncPC expression creation from the depths of walk to a
typecheck helper so it can be reused in both places.
For #61577.
Change-Id: I76f333157cf0e5fd867b41bfffcdaf6f45254707
Reviewed-on: https://go-review.googlesource.com/c/go/+/539698 Reviewed-by: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>