Support symbol versioning

Bug: http://b/20139821
Change-Id: I64122a0fb0960c20b2ce614161b7ab048456b681
diff --git a/linker/dlfcn.cpp b/linker/dlfcn.cpp
index 5ed8891..057c217 100644
--- a/linker/dlfcn.cpp
+++ b/linker/dlfcn.cpp
@@ -100,7 +100,7 @@
   }
 
   soinfo* found = nullptr;
-  ElfW(Sym)* sym = nullptr;
+  const ElfW(Sym)* sym = nullptr;
   void* caller_addr = __builtin_return_address(0);
   soinfo* caller = find_containing_library(caller_addr);