[Sema] Stable sort OverloadCandidates to remove non-deterministic ordering

Summary: This fixes failure in Misc/diag-template-diffing.cpp uncovered by D39245.

Reviewers: rjmccall, rsmith

Reviewed By: rjmccall

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D39944

llvm-svn: 318121

clang/lib/Sema/SemaOverload.cpp

@@ -10516,7 +10516,7 @@ void OverloadCandidateSet::NoteCandidates(
     }
   }
 
-  std::sort(Cands.begin(), Cands.end(),
+  std::stable_sort(Cands.begin(), Cands.end(),
             CompareOverloadCandidatesForDisplay(S, OpLoc, Args.size(), Kind));
 
   bool ReportedAmbiguousConversions = false;