[dev.ssa] cmd/compile/internal/ssa: allocate complex zero in the entry block
[dev.ssa] cmd/compile/internal/ssa: allocate complex zero in the entry block

Fixes build.  There may be no current block.

Change-Id: I0da8bab133dc207124556927698e7cd682e64ef5
Reviewed-on: https://go-review.googlesource.com/13989
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

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