message: Use std::nullptr_t instead of nullptr_t.
diff: // verilog/CST/verilog_treebuilder_utils.h that explains use
  // of std::forward in Make* helper functions.
  +#include <cstddef>
  #include <utility>
  #include <vector>
  @@ -58,7 +59,8 @@ verible::SymbolPtr MakeDPIImport(T0&& keyword, T1&& spec, T2&& property,
  // to deduce to that some paths are not reachble/applicable.
  template <typename T0, typename T1, typename T2, typename T3>
  verible::SymbolPtr MakeDPIImport(T0&& keyword, T1&& spec, T2&& property,
  - nullptr_t id, nullptr_t equals, T3&& proto) {
  + std::nullptr_t id, std::nullptr_t equals,
  + T3&& proto) {
  verible::CheckSymbolAsLeaf(*keyword, verilog_tokentype::TK_import);
  verible::CheckSymbolAsLeaf(*spec, verilog_tokentype::TK_StringLiteral);
  CHECK(verible::SymbolCastToNode(*proto).MatchesTagAnyOf(
  