cmd/link: add s390x to link tool main function
cmd/link: add s390x to link tool main function

Change-Id: I83bc2b4a00216b069f133113e4ae9ad76c98a708
Reviewed-on: https://go-review.googlesource.com/21741
Run-TryBot: Michael Munday <8f145917441a88646319703b14b4bef730f48765@ca.ibm.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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