runtime: more specific reason for skipping GDB tests on NetBSD
runtime: more specific reason for skipping GDB tests on NetBSD

Updates #22893.

Change-Id: I2cf5efb4fa6b77aaf82de5d8877c99f9aa5d519a
Reviewed-on: https://go-review.googlesource.com/81195
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

codestation/go,akutz/go,golang/go,CAFxX/go,Cofyc/go,akutz/go,nawawi/go,codestation/go,josharian/go,cloudflare/go,CAFxX/go,Cofyc/go,Cofyc/go,josharian/go,Cofyc/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,akutz/go,akutz/go,cloudflare/go,codestation/go,cloudflare/go,Cofyc/go,josharian/go,akutz/go,Cofyc/go,codestation/go,codestation/go,Cofyc/go,CAFxX/go,nawawi/go,akutz/go,golang/go,golang/go,codestation/go,golang/go,josharian/go,nawawi/go,codestation/go,josharian/go,nawawi/go,akutz/go,CAFxX/go,josharian/go,josharian/go,Cofyc/go,akutz/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,christopher-henderson/Go,nawawi/go,golang/go,cloudflare/go,codestation/go,josharian/go,golang/go,CAFxX/go,CAFxX/go,cloudflare/go