cmd/go: add a test for -sectcreate in LDFLAGS
cmd/go: add a test for -sectcreate in LDFLAGS

It was already covered by a regex pattern, but it didn't have a test.

To fix the issue for good, added regression test.

Fixes #28832.

Change-Id: I861e3bed92d3b9484fd8671270dbd2e264b10d2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/191311
Reviewed-by: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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