cmd/link: fix ARM gold linker check
cmd/link: fix ARM gold linker check

CL 23400 introduced a check to make sure the gold linker is used
on ARM host links. The check itself works, but the error checking
logic was reversed; fix it.

I manually verified that the check now correctly rejects host links
on my RPi2 running an ancient rasbian without the gold linker
installed.

Updates #15696

Change-Id: I927832620f0a60e91a71fdedf8cbd2550247b666
Reviewed-on: https://go-review.googlesource.com/23421
Run-TryBot: Elias Naur <993af7099cb24ce1a88d64108ae1e8b0385f2fc0@gmail.com>
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

derekmarcotte/go,momchil-velikov/go,suncycheng/go,CAFxX/go,cloudflare/go,CAFxX/go,codestation/go,vsekhar/elastic-go,cloudflare/go,ImJasonH/go,derekmarcotte/go,nawawi/go,nawawi/go,ImJasonH/go,goodlang/good,theif519/go,CAFxX/go,cloudflare/go,4ad/go,ImJasonH/go,momchil-velikov/go,golang/go,theif519/go,derekmarcotte/go,goodlang/good,goodlang/good,theif519/go,josharian/go,polyverse-security/go,vsekhar/elastic-go,codestation/go,akutz/go,momchil-velikov/go,Cofyc/go,theif519/go,goodlang/good,Cofyc/go,CAFxX/go,polyverse-security/go,vsekhar/elastic-go,vsekhar/elastic-go,ImJasonH/go,derekmarcotte/go,derekmarcotte/go,ImJasonH/go,vsekhar/elastic-go,4ad/go,golang/go,suncycheng/go,ImJasonH/go,momchil-velikov/go,suncycheng/go,Cofyc/go,suncycheng/go,goodlang/good,linux-on-ibm-z/go,codestation/go,4ad/go,Cofyc/go,goodlang/good,goodlang/good,suncycheng/go,Cofyc/go,akutz/go,momchil-velikov/go,codestation/go,ImJasonH/go,golang/go,linux-on-ibm-z/go,4ad/go,vsekhar/elastic-go,josharian/go,cloudflare/go,polyverse-security/go,codestation/go,golang/go,nawawi/go,codestation/go,derekmarcotte/go,Cofyc/go,polyverse-security/go,josharian/go,ImJasonH/go,golang/go,Cofyc/go,linux-on-ibm-z/go,linux-on-ibm-z/go,polyverse-security/go,suncycheng/go,nawawi/go,josharian/go,theif519/go,linux-on-ibm-z/go,cloudflare/go,suncycheng/go,theif519/go,codestation/go,golang/go,akutz/go,christopher-henderson/Go,nawawi/go,golang/go,momchil-velikov/go,derekmarcotte/go,polyverse-security/go,akutz/go,polyverse-security/go,Cofyc/go,derekmarcotte/go,nawawi/go,CAFxX/go,cloudflare/go,codestation/go,akutz/go,4ad/go,CAFxX/go,suncycheng/go,josharian/go,akutz/go,4ad/go,vsekhar/elastic-go,momchil-velikov/go,4ad/go,linux-on-ibm-z/go,nawawi/go,vsekhar/elastic-go,josharian/go,goodlang/good,josharian/go,polyverse-security/go,golang/go,CAFxX/go,akutz/go,theif519/go,momchil-velikov/go,akutz/go,nawawi/go,josharian/go,linux-on-ibm-z/go,cloudflare/go,4ad/go,linux-on-ibm-z/go,CAFxX/go,theif519/go,cloudflare/go