Fix date_time.hpp error and header generator warnings

[dwithun-dev]

What does this change do?

Is it related to an exisiting bug report or feature request?

Pre-merge checklist

• I've read CONTRIBUTING.md
• I've rebased my changes against the current HEAD of origin/master (if necessary)
• I've added new test cases to verify my change
• I've regenerated toml.hpp (how-to)
• I've updated any affected documentation
• I've rebuilt and run the tests with at least one of:
  • Clang 8 or higher
  • GCC 8 or higher
  • MSVC 19.20 (Visual Studio 2019) or higher
• I've added my name to the list of contributors in README.md

[dwithun-dev]

Sorry, I was trying to figure out where this goes (if it goes somewhere):

It came from the header generator.
Potentially missing #undefs:
#undef TOML_DISABLE_CONDITIONAL_NOEXCEPT_LAMBDA
#undef TOML_DISABLE_NOEXCEPT_NOEXCEPT

The second pull request I created, I realized I forgot to run the tests so I went back and tested and got some errors and fixed it maybe, by just removing line 7 and 8 from date_and_time.hpp

[marzer]

Ah, right. Yep, they need to go here: https://github.com/marzer/tomlplusplus/blob/master/tools%2Fgenerate_single_header.py#L206

Looks like some past contribution didn't add them, and I didn't catch it at the time.

[dwithun-dev]

Hey I updated the header generator how do I PR it into this same PR thread?

[dwithun-dev]

Done

[marzer]

Looks good, thanks! 🎉