fix gobuild.

errors introduced in CL 30601

R=austin
DELTA=6  (3 added, 0 deleted, 3 changed)
OCL=30663
CL=30665

src/cmd/gobuild/gobuild.go

@@ -71,8 +71,9 @@ func PushPkg(vp *[]*Pkg, p *Pkg) {
 		}
 		v = a;
 	}
-	*vp = v[0:n+1];
+	v = v[0:n+1];
 	v[n] = p;
+	*vp = v;
 }
 
 func PushFile(vp *[]*File, p *File) {
@@ -86,8 +87,9 @@ func PushFile(vp *[]*File, p *File) {
 		}
 		v = a;
 	}
-	*vp = v[0:n+1];
+	v = v[0:n+1];
 	v[n] = p;
+	*vp = v;
 }
 
 // For sorting Files

src/cmd/gobuild/util.go

@@ -82,8 +82,9 @@ func PushString(vp *[]string, p string) {
 		}
 		v = a;
 	}
-	*vp = v[0:n+1];
+	v = v[0:n+1];
 	v[n] = p;
+	*vp = v;
 }
 
 func run(argv []string, flag int) (ok bool) {