[dev.typeparams] runtime: allow newproc split stack

newproc was not allowed to split stack because it had a special
stack layout, where the go'd function's arguments were passed on
stack but not included in the signature (therefore the stack map).
Now it no longer has argument, so it does not need to be nosplit.

Change-Id: I6f39730fb1595c4b0438c74118fef418fe1c082b
Reviewed-on: https://go-review.googlesource.com/c/go/+/325919


Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>