[clang] error: attribute 'nothrow' cannot be applied to 'function'

For some reason pragma attribute push for nothrow doesn't work.

```c
#pragma clang attribute push(__attribute__((nothrow)), apply_to=function)

int foo() {
return 42;
}

#pragma clang attribute pop
```

https://godbolt.org/z/s6j8xe5Ej

```
:1:15: error: attribute 'nothrow' cannot be applied to 'function'
1 | #pragma clang attribute push(__attribute__((nothrow)), apply_to=function)
| ^ ~~~~~~~~
:1:45: warning: unused attribute 'nothrow' in '#pragma clang attribute push' region [-Wpragma-clang-attribute]
1 | #pragma clang attribute push(__attribute__((nothrow)), apply_to=function)
| ^
:7:15: note: '#pragma clang attribute push' regions ends here
7 | #pragma clang attribute pop
| ^
1 warning and 1 error generated.
Compiler returned: 1
```

Start by reproducing the diagnostic with the C snippet in the issue and compare the behavior in the linked Godbolt example. Trace Clang's pragma-attribute handling and attribute applicability checks; done means the pragma accepts nothrow for functions without the reported error or unused-attribute warning, with coverage for the example behavior.

Written by the indexing model from the issue text.