[sanitizer][Darwin] Suppress -Wno-non-virtual-dtor warning

[yln]

Summary

Suppress the warning:

'fake_shared_weak_count' has virtual functions but non-virtual destructor [-Wnon-virtual-dtor]

The warning has been recently enabled [1], but the associated cleanup
missed this instance in Darwin code [2].

[1] 9c31e12609e1935eb84a2497ac08a49e3139859a
[2] d48f2d7c02743571075bb7812bb4c9e634e51ed1

compiler-rt/lib/tsan/rtl/tsan_interceptors_mac.cpp

 struct fake_shared_weak_count {
   volatile a64 shared_owners;
   volatile a64 shared_weak_owners;
   virtual void _unused_0x0() = 0;
   virtual void _unused_0x8() = 0;
   virtual void on_zero_shared() = 0;
   virtual void _unused_0x18() = 0;
   virtual void on_zero_shared_weak() = 0;
+  virtual ~fake_shared_weak_count() = 0;  // suppress -Wnon-virtual-dtor
 };
 }  // namespace
 
 // The following code adds libc++ interceptors for:
 //     void __shared_weak_count::__release_shared() _NOEXCEPT;
 //     bool __shared_count::__release_shared() _NOEXCEPT;
 // Shared and weak pointers in C++ maintain reference counts via atomics in
 // libc++.dylib, which are TSan-invisible, and this leads to false positives in