Disable empty propagation if compiling as Objective-C++ to allow succ…

[Rajveer86]

…essful compilation of non-copyable callables

@Naios

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What was a problem?

Non-copyable lambdas failed to compile in Objective-C++.

How this PR fixes the problem?

This PR disables the bool() operator optimisation if the class is being compiled as Objective-C++.

Check lists (check x in [ ] of list items)

• Additional Unit Tests were added that test the feature or regression
• Coding style (Clang format was applied)

Additional Comments (if any)

Not sure how to add a unit test since it would require compiling as Objective-C++.

[Naios]

I would prefer to improve the corresponding code in the empty bool propagation rather than making the behaviour dependent on the current build language since a change in the behaviour without explicit specification is a no-go.

[Naios]

I will close this as elaborated above and in #29.
Feel free to open a new PR if you found a fix for the non working operator bool detection trait in Objective+C++.