[clang][Interp][NFC] Add some assertions

Make sure we pass a non-null Descriptor when creating a new Block.

Author: tbaederr

clang/lib/AST/Interp/InterpBlock.h

@@ -51,11 +51,15 @@ class Block final {
   /// Creates a new block.
   Block(const std::optional<unsigned> &DeclID, const Descriptor *Desc,
         bool IsStatic = false, bool IsExtern = false)
-      : DeclID(DeclID), IsStatic(IsStatic), IsExtern(IsExtern), Desc(Desc) {}
+      : DeclID(DeclID), IsStatic(IsStatic), IsExtern(IsExtern), Desc(Desc) {
+        assert(Desc);
+      }
 
   Block(const Descriptor *Desc, bool IsStatic = false, bool IsExtern = false)
       : DeclID((unsigned)-1), IsStatic(IsStatic), IsExtern(IsExtern),
-        Desc(Desc) {}
+        Desc(Desc) {
+          assert(Desc);
+        }
 
   /// Returns the block's descriptor.
   const Descriptor *getDescriptor() const { return Desc; }