[weak vtables] Remove a bunch of weak vtables

This patch removes most of the trivial cases of weak vtables by pinning them to
a single object file. The memory leaks in this version have been fixed. Thanks
Alexey for pointing them out.

Differential Revision: http://llvm-reviews.chandlerc.com/D2068

Reviewed by Andy

llvm-svn: 195064
diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 35808a6..62a3b31 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -735,9 +735,5 @@
 #endif
 }
 
-// Default implementation for CallbackVH.
-void CallbackVH::allUsesReplacedWith(Value *) {}
-
-void CallbackVH::deleted() {
-  setValPtr(NULL);
-}
+// Pin the vtable to this file.
+void CallbackVH::anchor() {}