Normally, a panic/throw only shows the thread stack for the current thread
and all paused goroutines. Goroutines running on other threads, or other threads
running on their system stacks, are opaque. Change that when GODEBUG=crash,
by passing a SIGQUIT around to all the threads when GODEBUG=crash.
If this works out reasonably well, we might make the SIGQUIT relay part of
the standard panic/throw death, perhaps eliding idle m's.

Change-Id: If7dd354f7f3a6e326d17c254afcf4f7681af2f8b
Reviewed-on: https://go-review.googlesource.com/2811
Reviewed-by: Rick Hudson <rlh@golang.org>

Fixes build on plan9 and windows.

Change-Id: Ic9b02c641ab84e4f6d8149de71b9eb495e3343b2
Reviewed-on: https://go-review.googlesource.com/2233
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

includes undo of 22318cd31d7d and also:
- always use SetUnhandledExceptionFilter on windows-386;
- crash when receive EXCEPTION_BREAKPOINT in exception handler.

Fixes #8006.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/155360043

That was complete failure - builders are broken,
but original cl worked fine on my system.
I will need access to builders
to test this change properly.

««« original CL description
runtime: handle all windows exception

Fixes #8006.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/145150043
»»»

TBR=rsc
R=golang-codereviews
CC=golang-codereviews
https://golang.org/cl/154180043

Fixes #8006.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/145150043

This is to simplify VEH handler before making
changes to fix issue 8006.

Update #8006

LGTM=adg, rsc
R=golang-codereviews, adg, rsc
CC=golang-codereviews
https://golang.org/cl/138630043

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.