Ciro Santilli b47efd35fb
Use defined for some preprocessor variables that might be undefined (#2476)
The variables PYBIND11_HAS_OPTIONAL, PYBIND11_HAS_EXP_OPTIONAL, PYBIND11_HAS_VARIANT,
__clang__, __APPLE__ were not checked for defined in a minortity of instances.

If the project using pybind11 sets -Wundef, the warnings will show.

The test build is also modified to catch the problem.
2020-09-10 13:58:26 -04:00
..
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