[clang] Change set type used for SourceLocation.

This is part of a patch series working towards the ability to make
SourceLocation into a 64-bit type to handle larger translation units.

If clang is built for a 32-bit platform and SourceLocation is 64 bits
wide, then a SourceLocation will be larger than a pointer, so it won't
be possible to keep them in a SmallPtrSet any more. Switch to
SmallDenseSet instead.

Patch originally by Mikhail Maltsev.

Differential Revision: https://reviews.llvm.org/D105493

clang/include/clang/Basic/SourceLocation.h

@@ -16,7 +16,6 @@
 
 #include "clang/Basic/LLVM.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Support/PointerLikeTypeTraits.h"
 #include <cassert>
 #include <cstdint>
 #include <string>
@@ -510,20 +509,6 @@ namespace llvm {
     static void Profile(const clang::SourceLocation &X, FoldingSetNodeID &ID);
   };
 
-  // Teach SmallPtrSet how to handle SourceLocation.
-  template<>
-  struct PointerLikeTypeTraits<clang::SourceLocation> {
-    static constexpr int NumLowBitsAvailable = 0;
-
-    static void *getAsVoidPointer(clang::SourceLocation L) {
-      return L.getPtrEncoding();
-    }
-
-    static clang::SourceLocation getFromVoidPointer(void *P) {
-      return clang::SourceLocation::getFromRawEncoding((unsigned)(uintptr_t)P);
-    }
-  };
-
 } // namespace llvm
 
 #endif // LLVM_CLANG_BASIC_SOURCELOCATION_H

clang/include/clang/Lex/Preprocessor.h

@@ -783,8 +783,7 @@ private:
   /// deserializing from PCH, we don't need to deserialize identifier & macros
   /// just so that we can report that they are unused, we just warn using
   /// the SourceLocations of this set (that will be filled by the ASTReader).
-  /// We are using SmallPtrSet instead of a vector for faster removal.
-  using WarnUnusedMacroLocsTy = llvm::SmallPtrSet<SourceLocation, 32>;
+  using WarnUnusedMacroLocsTy = llvm::SmallDenseSet<SourceLocation, 32>;
   WarnUnusedMacroLocsTy WarnUnusedMacroLocs;
 
   /// A "freelist" of MacroArg objects that can be