cmd/compile: simplify sharedProgArray init
cmd/compile: simplify sharedProgArray init

Per code review feedback on CL 40693.

Change-Id: I38c522022a3c2f3e61ea90181391edb5c178916e
Reviewed-on: https://go-review.googlesource.com/41300
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

cloudflare/go,cloudflare/go,golang/go,josharian/go,golang/go,cloudflare/go,vsekhar/elastic-go,christopher-henderson/Go,akutz/go,vsekhar/elastic-go,nawawi/go,ImJasonH/go,Cofyc/go,polyverse-security/go,vsekhar/elastic-go,nawawi/go,polyverse-security/go,codestation/go,ImJasonH/go,polyverse-security/go,CAFxX/go,derekmarcotte/go,nawawi/go,josharian/go,ImJasonH/go,josharian/go,cloudflare/go,nawawi/go,polyverse-security/go,nawawi/go,codestation/go,nawawi/go,ImJasonH/go,derekmarcotte/go,vsekhar/elastic-go,golang/go,CAFxX/go,polyverse-security/go,cloudflare/go,cloudflare/go,codestation/go,josharian/go,golang/go,akutz/go,codestation/go,derekmarcotte/go,cloudflare/go,derekmarcotte/go,vsekhar/elastic-go,Cofyc/go,akutz/go,codestation/go,Cofyc/go,codestation/go,akutz/go,vsekhar/elastic-go,ImJasonH/go,golang/go,Cofyc/go,ImJasonH/go,polyverse-security/go,vsekhar/elastic-go,CAFxX/go,akutz/go,derekmarcotte/go,CAFxX/go,josharian/go,Cofyc/go,polyverse-security/go,CAFxX/go,ImJasonH/go,Cofyc/go,Cofyc/go,codestation/go,vsekhar/elastic-go,akutz/go,derekmarcotte/go,josharian/go,nawawi/go,codestation/go,golang/go,derekmarcotte/go,polyverse-security/go,ImJasonH/go,Cofyc/go,cloudflare/go,josharian/go,josharian/go,golang/go,CAFxX/go,akutz/go,akutz/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,derekmarcotte/go