wpiutil: Replace LLVM Optional with C++17-compatible optional

Imported from https://github.com/akrzemi1/Optional with minor changes:
- Compiler conditional simplifications (we only use recent versions)
- Move from std::experimental to wpi namespace
- Change tests to integrate with Google Test

Update LLVM use cases.
This commit is contained in:
Peter Johnson
2018-11-19 22:57:34 -08:00
parent 489701cacc
commit 0b03454366
14 changed files with 2494 additions and 422 deletions

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