cmd/internal/obj: generate SEH aux symbols for windows/amd64

cmd/internal/obj: generate SEH aux symbols for windows/amd64

This CL updates the Go compiler so it generate SEH unwind info [1] as a
function auxiliary symbol when building for windows/amd64.

A follow up CL will teach the Go linker how to assemble these codes
into the PE .xdata section.

Updates #57302

[1] https://learn.microsoft.com/en-us/cpp/build/exception-handling-x64#struct-unwind_info

Change-Id: I40ae0437bfee326c1a67c2b5e1496f0bf3ecea17
Reviewed-on: https://go-review.googlesource.com/c/go/+/461749
Reviewed-by: Davis Goodin <dagood@microsoft.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>