Add !callees metadata

This patch adds a new kind of metadata that indicates the possible callees of
indirect calls.

Differential Revision: https://reviews.llvm.org/D37354

llvm-svn: 315944
diff --git a/llvm/lib/IR/LLVMContext.cpp b/llvm/lib/IR/LLVMContext.cpp
index 455ffb5..a94da54 100644
--- a/llvm/lib/IR/LLVMContext.cpp
+++ b/llvm/lib/IR/LLVMContext.cpp
@@ -59,6 +59,7 @@
     {MD_section_prefix, "section_prefix"},
     {MD_absolute_symbol, "absolute_symbol"},
     {MD_associated, "associated"},
+    {MD_callees, "callees"},
   };
 
   for (auto &MDKind : MDKinds) {