internal/version: ignore signals intended for the child process

Since the underlying toolchain is run as a child process (and not
exec'd), signals that are sent to this process (for example, an
interrupt sent by a shell) will be handled by both the parent and the
child. This poses a problem for signals like SIGQUIT, where both
processes' runtimes attempt to write out information to the same output.

Before running the final command, start a signal handler that will
ignore a signal sent to the parent, emulating the behavior of go run.

This code is a modified version of cmd/go/internal/base.

Fixes golang/go#36976.

Change-Id: I29aa699dc059fd448aa9478f729ed8d90379616b
Reviewed-on: https://go-review.googlesource.com/c/dl/+/217765
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>