Paul Fultz II 8519a1411c Fix helper header when using c++17 (#1666) ...

This will fix issue #1621. It also adds tests for is_callable with c++11, c++14, and c++17.

The fallback implementation was completely broken so I rewrote it so it pass the tests as well. This should be used instead of PR #1631.

2019-11-20 21:33:42 +05:30

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hip

Fix helper header when using c++17 (#1666)

2019-11-20 21:33:42 +05:30