Some C++11 msvc-specific attributes are not supported by clang ast

[RIscRIpt]

• [[msvc::no_tls_guard]] from MSVC 14.25.28610
• [[msvc::known_semantics]] from MSVC 14.27.29110
• [[msvc::noop_dtor]] from MSVC 14.28.29333
• [[msvc::constexpr]] from MSVC 14.33.31629

Edit: I'll try to provide a patch.

[RIscRIpt]

As per discussion in D133853, noop attributes are not welcome in clang.

Unfortunately, due to lack of proper documentation, I abandon my attempts to add support of first three attributes:

• [[msvc::no_tls_guard]]
• [[msvc::known_semantics]]
• [[msvc::noop_dtor]]

Regarding [[msvc::constexpr]] - it is under review (and consideration) in D134475 #71300