cmd/compile: don't emit inltree for closure within body of inlined func

When inlining functions with closures, ensure that we don't mark the
body of the closure with a src.Pos marker that reflects the inline,
since this will result in the generation of an inltree table for the
closure itself (as opposed to the routine that the func-with-closure
was inlined into).

Fixes #46234.

Change-Id: I348296de6504fc4745d99adab436640f50be299a
Reviewed-on: https://go-review.googlesource.com/c/go/+/320913


Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Than McIntosh <thanm@google.com>