[NFC][AliasSetTracker] Remove implicit conversion AliasResult to integer.

[dfukalov]

Summary

Preparation to make AliasResult scoped enumeration.

[nikic]

LGTM

llvm/lib/Analysis/AliasSetTracker.cpp

 /// alias the pointer. Return the unified set, or nullptr if no set that aliases
 /// the pointer was found. MustAliasAll is updated to true/false if the pointer
 /// is found to MustAlias all the sets it merged.
 AliasSet *AliasSetTracker::mergeAliasSetsForPointer(const Value *Ptr,
                                                     LocationSize Size,
                                                     const AAMDNodes &AAInfo,
                                                     bool &MustAliasAll) {
   AliasSet *FoundSet = nullptr;
-  AliasResult AllAR = MustAlias;
+  MustAliasAll = true;
   for (AliasSet &AS : llvm::make_early_inc_range(*this)) {
     if (AS.Forward)
       continue;
 
     AliasResult AR = AS.aliasesPointer(Ptr, Size, AAInfo, AA);
     if (AR == NoAlias)
       continue;
 
-    AllAR =
-        AliasResult(AllAR & AR); // Possible downgrade to May/Partial, even No
+    if (AR != MustAlias)
+      MustAliasAll = false;
 
     if (!FoundSet) {
       // If this is the first alias set ptr can go into, remember it.
       FoundSet = &AS;
     } else {
       // Otherwise, we must merge the sets.
       FoundSet->mergeSetIn(AS, *this);
     }
   }
 
-  MustAliasAll = (AllAR == MustAlias);
   return FoundSet;
 }
 
 AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
   AliasSet *FoundSet = nullptr;
   for (AliasSet &AS : llvm::make_early_inc_range(*this)) {
     if (AS.Forward || !AS.aliasesUnknownInst(Inst, AA))
       continue;