[clang] nonblocking/nonallocating attributes (was: nolock/noalloc) (PR #84983)

[Chris Apple via cfe-commits]

cjappl wrote:

I can confirm that now if I try to use any argument with `blocking` I get: 
```
/Users/topher/Desktop/test_radsan/main.cpp:25:40: error: 'blocking' attribute takes no arguments
   25 | float process (float* data) noexcept [[clang::blocking(false)]]
```

Great!

https://github.com/llvm/llvm-project/pull/84983