s/std::set/DenseSet/; NFC

We only use this set for `insert` and `count`, so a hashing container
seems better here.

llvm-svn: 340783

llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp

@@ -237,7 +237,7 @@ void splitAndWriteThinLTOBitcode(
   // sound because the virtual constant propagation optimizations effectively
   // inline all implementations of the virtual function into each call site,
   // rather than using function attributes to perform local optimization.
-  std::set<const Function *> EligibleVirtualFns;
+  DenseSet<const Function *> EligibleVirtualFns;
   // If any member of a comdat lives in MergedM, put all members of that
   // comdat in MergedM to keep the comdat together.
   DenseSet<const Comdat *> MergedMComdats;