cmd/link: give RelocVariant a type, document Reloc
cmd/link: give RelocVariant a type, document Reloc

Change-Id: Ib20263405a08674b5e160295fc965da4c8b54b34
Reviewed-on: https://go-review.googlesource.com/29248
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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