misc/cgo/testshared: make -v output less verbose
misc/cgo/testshared: make -v output less verbose

Previously, 'go test -v' in this directory would result in a massive
dump of go command output, because the test plumbed -v to 'build -x'.
This change separates them into distinct flags, so that '-v' only
implies the display of default 'go' command output.

Updates #30316

Change-Id: Ifb125f35ec6a0bebe7e8286e7c546d132fb213df
Reviewed-on: https://go-review.googlesource.com/c/go/+/208232
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

cloudflare/go,nawawi/go,cloudflare/go,CAFxX/go,CAFxX/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go,CAFxX/go,akutz/go,akutz/go,golang/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,golang/go,cloudflare/go,akutz/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,nawawi/go,nawawi/go,akutz/go,nawawi/go,akutz/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,golang/go,nawawi/go,akutz/go