cmd/compile/internal/gc: fix the build

Commit acc90c53 passed the trybots, lingered for weeks, and in the
meantime the type of this variable changed to a bool. I didn't rebase
and re-run the trybots before submitting.

Fixes #12832

Change-Id: If24fda227edd8207f8069c67f1c45f08e6ac215a
Reviewed-on: https://go-review.googlesource.com/15286Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -2986,7 +2986,7 @@ func implements(t *Type, iface *Type, m **Type, samename **Type, ptr *int) bool
 	var followptr bool
 	var rcvr *Type
 	for im := iface.Type; im != nil; im = im.Down {
-		if im.Broke == 1 {
+		if im.Broke {
 			continue
 		}
 		imtype = methodfunc(im.Type, nil)