cmd/compile: remove unused global variable loophack

Old parser remains.

Change-Id: I05ef1737802e23afc2c2129f58cb66feef8e3425
Reviewed-on: https://go-review.googlesource.com/17244Reviewed-by: David Crawshaw <crawshaw@golang.org>

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

@@ -599,8 +599,6 @@ var incannedimport int
 
 var statuniqgen int // name generator for static temps
 
-var loophack bool
-
 var iota_ int32
 
 var lastconst *NodeList