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 <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/gsubr.go

@@ -37,11 +37,7 @@ import (
 	"cmd/internal/src"
 )
 
-var sharedProgArray *[10000]obj.Prog // *T instead of T to work around issue 19839
-
-func init() {
-	sharedProgArray = new([10000]obj.Prog)
-}
+var sharedProgArray *[10000]obj.Prog = new([10000]obj.Prog) // *T instead of T to work around issue 19839
 
 // Progs accumulates Progs for a function and converts them into machine code.
 type Progs struct {