[clang][Interp][NFC] Add const InterpBlock::deref() overload

Author: tbaederr

clang/lib/AST/Interp/Interp.h

@@ -1004,7 +1004,7 @@ bool SetThisField(InterpState &S, CodePtr OpPC, uint32_t I) {
 
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool GetGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
-  auto *B = S.P.getGlobal(I);
+  const Block *B = S.P.getGlobal(I);
   if (B->isExtern())
     return false;
   S.Stk.push<T>(B->deref<T>());

clang/lib/AST/Interp/InterpBlock.h

@@ -98,6 +98,9 @@ class Block final {
   /// Returns a view over the data.
   template <typename T>
   T &deref() { return *reinterpret_cast<T *>(data()); }
+  template <typename T> const T &deref() const {
+    return *reinterpret_cast<const T *>(data());
+  }
 
   /// Invokes the constructor.
   void invokeCtor() {