robs bug converting unsafe.pointer

R=r
OCL=20834
CL=20834

src/cmd/gc/go.h

@@ -156,6 +156,7 @@ struct	Type
 	uchar	embedded;	// TFIELD embedded type
 	uchar	siggen;
 	uchar	funarg;
+	uchar	copyany;
 
 	// TFUNCT
 	uchar	thistuple;

src/cmd/gc/subr.c

@@ -1779,6 +1779,8 @@ loop:
 		goto loop;
 
 	case TANY:
+		if(!st->copyany)
+			return 0;
 		*stp = t;
 		break;
 
@@ -1841,6 +1843,11 @@ deep(Type *t)
 		nt = t;	// share from here down
 		break;
 
+	case TANY:
+		nt = shallow(t);
+		nt->copyany = 1;
+		break;
+
 	case TPTR32:
 	case TPTR64:
 	case TCHAN: