cmd/link: tidy up rdsym
cmd/link: tidy up rdsym

Use an early return. Check errors. Deduplicate.

Change-Id: Iabefd563b5ef82a16fab4791277630804fd09003
Reviewed-on: https://go-review.googlesource.com/20597
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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