Add a doxygen comment for this class.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124480 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/MergeFunctions.cpp

@@ -90,6 +90,8 @@ static unsigned ProfileFunction(const Function *F) {
 
 namespace {
 
+/// ComparableFunction - A struct that pairs together functions with a
+/// TargetData so that we can keep them together as elements in the DenseSet.
 class ComparableFunction {
 public:
   static const ComparableFunction EmptyKey;