cmd/cgo/internal/testcshared: remove an arbitrary timeout in TestSignalHandlersWithNotify

cmd/cgo/internal/testcshared: remove an arbitrary timeout in TestSignalHandlersWithNotify

Also log verbose information when -test.v is set.

We need an arbitrary delay when checking that a signal is *not*
delivered, but when we expect the signal to arrive we don't need to
set an arbitrary limit on how long that can take.

Fixes #61264.

Change-Id: If3bbbf78e3c22694bf825d90d7ee9564ce8daedd
Reviewed-on: https://go-review.googlesource.com/c/go/+/509636
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>