[polly] Define PointerLikeTypeTraits as struct in response to related llvm change

[mgrang]

Summary

This patch is in response to D35043 which changed "class PointerLikeTypeTraits" to "struct PointerLikeTypeTraits". Without this patch, we get a warning due to mismatching definitions of PointerLikeTypeTraits.

[grosser]

LGTM.

[mgrang]

I see this has already been done in https://reviews.llvm.org/rL310667. My sources seem to have been outdated. Abandoning this one.

include/polly/CodeGen/IslExprBuilder.h

 class DataLayout;
 class ScalarEvolution;
 } // namespace llvm
 
 struct isl_id;
 
 namespace llvm {
 // Provide PointerLikeTypeTraits for isl_id.
-template <> class PointerLikeTypeTraits<isl_id *> {
+template <> struct PointerLikeTypeTraits<isl_id *> {
 
 public:
   static inline const void *getAsVoidPointer(isl_id *P) { return (void *)P; }
   static inline const Region *getFromVoidPointer(void *P) {
     return (Region *)P;
   }
   enum { NumLowBitsAvailable = 0 };
 };