sync/atomic: add s390x implementations of atomic functions
sync/atomic: add s390x implementations of atomic functions

Load and store instructions are atomic on s390x.

Change-Id: I33c641a75954f4fbd301b11a467cb57872038880
Reviewed-on: https://go-review.googlesource.com/20947
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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