runtime: don't check sigaltstack on darwin/{arm,arm64}
runtime: don't check sigaltstack on darwin/{arm,arm64}

Use of the alternate signal stack on darwin/{arm,arm64} is reportedly
buggy, and the runtime function sigaltstack does nothing.  So don't
check the sigaltstack result to decide how to handle the signal stack.

Fixes #14070.

Change-Id: Ie97ede8895fad721e3acc79225f2cafcbe1f3a81
Reviewed-on: https://go-review.googlesource.com/18940
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Minux Ma <72d850dbd8858b791995463d8539b5a379577f28@golang.org>

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