Fix weak function lookups

* Linker now correctly resolves function defined
   with __attribute__((weak)).

Bug: https://code.google.com/p/android/issues/detail?id=70206
Change-Id: I82efb905676c25fefb1b11a13f5fecb0f1384657

tests/libs/dlsym_weak_function.cpp

@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+extern "C" int __attribute__((weak)) weak_func() {
+  return 42;
+}
+