Add compilation test instead of VxWorks checkHEADdev

`<future>` is explicitly excluded for VxWork, because enabling it causes
compilation error when building tests (and causes some serious issues
when trying to naively work-arond this compilation problem). When
forcing `QT_FEATURE_cxx11_future` on VxWorks, failure occurs:

```
qtbase/src/corelib/thread/qthread.h:125:19: error: no matching function for call to 'invoke'
  125 |             (void)std::invoke(std::move(f), std::forward<decltype(largs)>(largs)...);
      |                   ^~~~~~~~~~~

[...]
qtbase/tests/auto/corelib/thread/qpromise/snippet_qpromise.cpp:32:45: note: in instantiation of function template specialization 'QThread::create<(lambda at qtbase/tests/auto/corelib/thread/qpromise/snippet_qpromise.cpp:32:52), QPromise<int>>' requested here
   32 |     QScopedPointer<QThread> thread(QThread::create([] (QPromise<int> promise) {
      |                                             ^
VSB/usr/h/public/type_traits:2720:7: note: candidate template ignored: substitution failure [with _Callable = remove_reference_t<(lambda at qtbase/tests/auto/corelib/thread/qpromise/snippet_qpromise.cpp:32:52) &>, _Types = <QPromise<int> &>]: no matching function for call to '_Call'
 2720 |         auto invoke(_Callable&& _Obj, _Types&&... _Args) noexcept(noexcept(_Invoker<_Callable, _Types...>::_Call(
      |              ^
 2721 |                 _STD forward<_Callable>(_Obj), _STD forward<_Types>(_Args)...)))
 2722 |         -> decltype(_Invoker<_Callable, _Types...>::_Call(
      |                     ~~~~~~~~
```

Instead of excluding cxx11_future on VxWorks explicitly, replace
condition with actual check which should pass in non-VxWorks 24.03 (or
older) standard libraries.

VxWorks in version 24.03 fails this test due to std::async improperly
forwards argument type to lambda, which causes compilation error when
argument type is a non-copiable value type. This is a problem in VxWorks
standard library, which could be fixed in future versions of this OS, so
keeping this as a test should unlock `<future>` header once it's fixed.

Pick-to: 6.7
Task-number: QTBUG-115777
Change-Id: Ic67df9be2e95dce999689eaea146f113017ab4f3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

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