[dev.regabi] cmd/compile: call NeedFuncSym in InitLSym

InitLSym is where we're now generating ABI wrappers, so it seems as
good a place as any to make sure we're generating the degenerate
closure wrappers for declared functions and methods.

Change-Id: I097f34bbcee65dee87a97f9ed6f3f38e4cf2e2b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/283312


Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>