runtime: crash earlier on windows for runtime.abort

The isAbort check was wrong for non-x86 systems.
That was causing the exception chain to be passed back to Windows.
That was causing some other kind of fault - not sure what.
That was leading back to lastcontinuehandler to print a larger
stack trace, and then the throwing = 1 print added runtime.abort,
which made TestAbort pass even though it wasn't really working.

Recognize abort properly and handle it as Go, not as something
for Windows to try to handle.

Keep the throwing = 1 print, because more detail on throw is
always better.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.
This CL is, however, not windows/arm64-specific.
It is cleanup meant to make the port (and future ports) easier.

Change-Id: If614f4ab2884bd90410d29e28311bf969ceeac09
Reviewed-on: https://go-review.googlesource.com/c/go/+/288810


Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>