[clang] Don't mark _ReadBarrier(), _ReadWriteBarrier(), _WriteBarrier() deprecated

[thakis]

Summary

It's true that docs.microsoft.com says:

"""The _ReadBarrier, _WriteBarrier, and _ReadWriteBarrier compiler
intrinsics and the MemoryBarrier macro are all deprecated and should not
be used. For inter-thread communication, use mechanisms such as
atomic_thread_fence and std::atomic<T>, which are defined in the C++
Standard Library. For hardware access, use the /volatile:iso compiler
option together with the volatile keyword."""

And these attributes have been here since these builtins were added in
r192860.

However:

• cl.exe does not warn on them even with /Wall
• none of the replacements are useful for C code
• we don't add attribute((deprecated())) to any other declarations in intrin.h
• intrin0.h in the MSVC headers declares _ReadWriteBarrier() (but without the deprecation attribute), so you get inconsistent deprecation warnings depending on if you include intrin.h or intrin0.h

The motivation is that compiling sqlite.h with clang-cl produces a
deprecation warning with clang-cl for _ReadWriteBarrier(), but not with
cl.exe.

[hans]

Sounds very reasonable to me. lgtm

clang/lib/Headers/intrin.h

 void *_InterlockedCompareExchangePointer_HLEAcquire(void *volatile *, void *,
                                                     void *);
 void *_InterlockedCompareExchangePointer_HLERelease(void *volatile *, void *,
                                                     void *);
 long _InterlockedExchangeAdd_HLEAcquire(long volatile *, long);
 long _InterlockedExchangeAdd_HLERelease(long volatile *, long);
 __int64 _InterlockedExchangeAdd64_HLEAcquire(__int64 volatile *, __int64);
 __int64 _InterlockedExchangeAdd64_HLERelease(__int64 volatile *, __int64);
-void __attribute__((__deprecated__(
-    "use other intrinsics or C++11 atomics instead"))) _ReadBarrier(void);
-void __attribute__((__deprecated__(
-    "use other intrinsics or C++11 atomics instead"))) _ReadWriteBarrier(void);
+void _ReadBarrier(void);
+void _ReadWriteBarrier(void);
 unsigned int _rorx_u32(unsigned int, const unsigned int);
 int _sarx_i32(int, unsigned int);
 #if __STDC_HOSTED__
 int __cdecl _setjmp(jmp_buf);
 #endif
 unsigned int _shlx_u32(unsigned int, unsigned int);
 unsigned int _shrx_u32(unsigned int, unsigned int);
 void _Store_HLERelease(long volatile *, long);
 void _Store64_HLERelease(__int64 volatile *, __int64);
 void _StorePointer_HLERelease(void *volatile *, void *);
-void __attribute__((__deprecated__(
-    "use other intrinsics or C++11 atomics instead"))) _WriteBarrier(void);
+void _WriteBarrier(void);
 unsigned __int32 xbegin(void);
 void _xend(void);
 
 /* These additional intrinsics are turned on in x64/amd64/x86_64 mode. */
 #ifdef __x86_64__
 void __addgsbyte(unsigned long, unsigned char);
 void __addgsdword(unsigned long, unsigned long);
 void __addgsqword(unsigned long, unsigned __int64);