Windows support: can't build

[Murad]

Visual Studio 2019 stdlib + clang 10.0 compilation fails because Microsoft uses __declspec(noreturn) in their internal stdlib public headers. When someone includes standards compliant stdnoreturn.h __decspec(noreturn) gets replaced by __declspec(_Noreturn). We possibly have to handle Windows clusterfuck separately if we want to take advantage of noreturn specificators.