Use llvm::stable_sort

Make some small adjustment while touching the code: make parameters
const, use less_first(), etc.

Differential Revision: https://reviews.llvm.org/D60989

llvm-svn: 358943
diff --git a/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp b/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp
index a9683d0..3845602 100644
--- a/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp
@@ -1014,11 +1014,10 @@
 // new undefines from libraries.
 void MachOLinkingContext::finalizeInputFiles() {
   std::vector<std::unique_ptr<Node>> &elements = getNodes();
-  std::stable_sort(elements.begin(), elements.end(),
-                   [](const std::unique_ptr<Node> &a,
-                      const std::unique_ptr<Node> &b) {
-                     return !isLibrary(a) && isLibrary(b);
-                   });
+  llvm::stable_sort(elements, [](const std::unique_ptr<Node> &a,
+                                 const std::unique_ptr<Node> &b) {
+    return !isLibrary(a) && isLibrary(b);
+  });
   size_t numLibs = std::count_if(elements.begin(), elements.end(), isLibrary);
   elements.push_back(llvm::make_unique<GroupEnd>(numLibs));
 }