runtime: fix TestGdbConst on windows
runtime: fix TestGdbConst on windows

Some (all?) versions of gdb on windows output "\r\n" as line ending
instead of "\n".

Fixes #22012

Change-Id: I798204fd9f616d6d2c9c28eb5227fadfc63c0d45
Reviewed-on: https://go-review.googlesource.com/65850
Reviewed-by: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>
Run-TryBot: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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