Add needed functions to glibc-compat for pkg

ports/glibc-compat/src/libc-symbols.h

Index: ports/glibc-compat/src/libc-symbols.h
diff --git a/ports/glibc-compat/src/libc-symbols.h b/ports/glibc-compat/src/libc-symbols.h
index 2c218ee462e4d6f80879d97fdf55df2ce0294b4f..c98c52eddd0c9fa3e0a57cea590ad73becc2fcfb 100644
--- a/ports/glibc-compat/src/libc-symbols.h
+++ b/ports/glibc-compat/src/libc-symbols.h
@@ -1,3 +1,8 @@
+/*
+ * Copyright 2015 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
 #ifndef _LIBC_SYMBOLS_H
 #define _LIBC_SYMBOLS_H 1
 
@@ -14,8 +19,9 @@
 #define DL_CALL_FCT(x,y) x y
 #define attribute_hidden
 #define internal_function
-
 #define __set_errno(x) (errno = (x))
+#define weak_alias(name, aliasname) _weak_alias (name, aliasname)
+#define _weak_alias(name, aliasname)                                  \
+  extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 
 #endif
-