[MergeFunc] Use less_first() as the comparator of Schwartzian transform

llvm-svn: 358738
diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index d0c1613..8a40f04 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -403,12 +403,7 @@
     }
   }
 
-  std::stable_sort(
-      HashedFuncs.begin(), HashedFuncs.end(),
-      [](const std::pair<FunctionComparator::FunctionHash, Function *> &a,
-         const std::pair<FunctionComparator::FunctionHash, Function *> &b) {
-        return a.first < b.first;
-      });
+  std::stable_sort(HashedFuncs.begin(), HashedFuncs.end(), less_first());
 
   auto S = HashedFuncs.begin();
   for (auto I = HashedFuncs.begin(), IE = HashedFuncs.end(); I != IE; ++I) {