runtime: avoid relying on the unwinder in deferreturn
This CL changes deferreturn so that it never needs to invoke the
unwinder. Instead, in the unusual case that we recover into a frame
with pending open-coded defers, we now save the extra state needed to
find them in g.param.
Change-Id: Ied35f6c1063fee5b6044cc37b2bccd3f90682fe6
Reviewed-on: https://go-review.googlesource.com/c/go/+/515856 Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>