cmd/gc: fix a spurious -u compile error

Fixes #4082.

R=dsymonds
CC=golang-dev
https://golang.org/cl/6545055
diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index eeb46e2..74ed84b 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -1536,9 +1536,7 @@
 		}
 	}
 
-	// TODO(rsc): should not need to check importpkg,
-	// but reflect mentions unsafe.Pointer.
-	if(safemode && !incannedimport && !importpkg && t && t->etype == TUNSAFEPTR)
+	if(safemode && !incannedimport && !importpkg && !compiling_wrappers && t && t->etype == TUNSAFEPTR)
 		yyerror("cannot use unsafe.Pointer");
 
 	evconst(n);