qt_internal_add_configure_time_executable compiles the executable
at configure time and exposes it to the CMake source tree. This is
useful when need to run a small C++ program at configure time.
Task-number: QTBUG-87480
Change-Id: I031efe797c8afa0721d75b46d4f36f67276bf46e
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>