[dev.regabi] cmd/compile: scan body of closure in tooHairy to check for disallowed nodes

Several of the bugs in #43818 are because we were not scanning the body
of an possibly inlined closure in tooHairy(). I think this scanning got
lost in the rebase past some of the ir changes. This fixes the issue
related to the SELRECV2 and the bug reported from cuonglm. There is at
least one other bug related to escape analysis which I'll fix in another
change.

Change-Id: I8f38cd12a287881155403bbabbc540ed5fc2248e
Reviewed-on: https://go-review.googlesource.com/c/go/+/285676


Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>