message: Work around older compilers that want a storage for a static constexpr.
  Use old-school enum constant instead.
diff: @@ -34,7 +34,7 @@ namespace verible {
  struct ExpectedTokenInfo : public TokenInfo {
  // This pseudo token_enum signals to the test harness to not bother
  // checking the token enum, and check only the string contents.
  - static constexpr int kDontCare = -1;
  + enum { kDontCare = -1 };
  ExpectedTokenInfo() : TokenInfo(TokenInfo::EOFToken()) {}
  