[CHERIoT] Minor change to fix warning in older clang versions

Author: xdoardo

clang/include/clang/AST/Stmt.h

@@ -639,7 +639,8 @@ class alignas(void *) Stmt {
     unsigned BasePathSize;
   };
 
-  static_assert(CK_IntToOCLSampler == (CastExprBitfields{.Kind = CK_IntToOCLSampler}).Kind,
+  static_assert(CK_IntToOCLSampler ==
+                    (CastExprBitfields{CK_IntToOCLSampler, 0, 0, 0}).Kind,
                 "Need more cast kind bits");
 
   class BinaryOperatorBitfields {