add a fortified implementation of getcwd

Change-Id: Ice3e6d3e1ff07788305dc85f8ee4059baad5fac4
diff --git a/libc/libc.map b/libc/libc.map
index 8c3ac9e..6117d53 100644
--- a/libc/libc.map
+++ b/libc/libc.map
@@ -1336,6 +1336,7 @@
   global:
     __fread_chk;
     __fwrite_chk;
+    __getcwd_chk;
     getgrgid_r;
     getgrnam_r;
 } LIBC;