There is another unexpected problem with Clang on Windows.
If I add "-std=c++17" to cpp options, then in case of GUI app (example: tutorial/Gui01) in Debug configuration I get this (Release is fine):
[code]Linking...
lld-link: error: duplicate symbol: std::__throw_bad_alloc()
>>> defined at c:\local\apps\upp\uppsrc\Core\heap.cpp:315
>>> c:/local/apps/upp/out/tutorial/Core/CLANGx64cpp17.Debug.Debu g_Full.Gui\heap.o
>>> defined at libc++.a(new.cpp.obj)

lld-link: error: duplicate symbol: operator new(unsigned long long)
>>> defined at c:\local\apps\upp\uppsrc\Core\heap.cpp:301
>>> c:/local/apps/upp/out/tutorial/Core/CLANGx64cpp17.Debug.Debu g_Full.Gui\heap.o
>>> defined at libc++.a(new.cpp.obj)