[Sema] Fix strict ordering in overload candidate comparisons

This is a follow-up to febf5c9 and
another instance of llvm#64121.

The added test only fails if Clang is built with libc++ and a enabled
debug check for strict weak ordering.

Author: ilya-biryukov

clang/lib/Sema/SemaOverload.cpp

@@ -12107,9 +12107,12 @@ struct CompareOverloadCandidatesForDisplay {
         if (RFailureKind != ovl_fail_bad_deduction)
           return true;
 
-        if (L->DeductionFailure.Result != R->DeductionFailure.Result)
-          return RankDeductionFailure(L->DeductionFailure)
-               < RankDeductionFailure(R->DeductionFailure);
+        if (L->DeductionFailure.Result != R->DeductionFailure.Result) {
+          unsigned LRank = RankDeductionFailure(L->DeductionFailure);
+          unsigned RRank = RankDeductionFailure(R->DeductionFailure);
+          if (LRank != RRank)
+            return LRank < RRank;
+        }
       } else if (RFailureKind == ovl_fail_bad_deduction)
         return false;
 

clang/test/SemaCXX/overloaded-operators-display-order-crash.cpp

@@ -52,3 +52,17 @@ namespace bad_conversion {
     // CHECK-NEXT: void func(double*, int, int)
   }
 }
+
+namespace bad_deduction {
+  template <class> struct templ {};
+  template <class T> void func(templ<T>);
+  template <class T> void func(T*);
+  template <class T> auto func(T&) -> decltype(T().begin());
+  template <class T> auto func(const T&) -> decltype(T().begin());
+
+  bool doit() {
+    struct record {} r;
+    func(r); // expected-error {{no matching function for call to 'func'}}
+             // expected-note@* 4{{candidate}}
+  }
+}