clang: suppress a warning

    lib/expr.c:380:28: warning: passing
          'const uint8_t *' (aka 'const unsigned char *') to parameter of type
          'const char *' converts between pointers to integer types with different
          sign [-Wpointer-sign]
      grn_bulk_write(ctx, obj, p, vs);
                               ^

lib/expr.c

@@ -377,7 +377,7 @@ grn_obj_unpack(grn_ctx *ctx, const uint8_t *p, const uint8_t *pe, uint8_t type,
     ERR(GRN_INVALID_FORMAT, "benced image is corrupt");
     return p;
   }
-  grn_bulk_write(ctx, obj, p, vs);
+  grn_bulk_write(ctx, obj, (const char *)p, vs);
   return p + vs;
 }