Starting with CMake 3.18, there is PCH support for darwin multi-arch
builds, like iOS simulator_and_device builds.
Also enable PCH for Objective-C++ files when the support is there.
To enable PCH for Objective-C++, we need to do enable the OBJCXX
language as well, but conditionally, because on non-darwin platforms
the language is probably not available.
Introduce the qt_enable_cmake_languages() macro which is called
automatically by qt_build_repo_begin().
Change-Id: I0e7f44be6577ac54ce940470036626409920e272
Reviewed-by: Leander Beernaert <leander.beernaert@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
430232e44d