linker: add dlvsym(3)

This changes implements dlvsym - dlsym for versioned symbols.

Bug: http://b/22865643
Change-Id: Ic90a60d512104261a1416c43f9100f0d88e3b46f
diff --git a/libdl/libdl.map.txt b/libdl/libdl.map.txt
index 8d123fe..55a03cb 100644
--- a/libdl/libdl.map.txt
+++ b/libdl/libdl.map.txt
@@ -32,6 +32,7 @@
   global:
     android_init_namespaces;
     android_create_namespace;
+    dlvsym;
 } LIBC;
 
 LIBC_PRIVATE {