runtime: make sync_atomic_SwapPointer signature match sync/atomic
runtime: make sync_atomic_SwapPointer signature match sync/atomic

SwapPointer is declared as

  func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)

in sync/atomic, but defined in the runtime (where it's actually
implemented) as

  func sync_atomic_SwapPointer(ptr unsafe.Pointer, new unsafe.Pointer) unsafe.Pointer

Make ptr a *unsafe.Pointer in the runtime definition to match the type
in sync/atomic.

Change-Id: I99bab651b995001bbe54f9e790fdef2417ef0e9e
Reviewed-on: https://go-review.googlesource.com/21998
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Michael Matloob <4562438b12c14e81a47550acde616ff328a909f8@golang.org>

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