Assume bounds cast fails for function pointers

[Machiry]

File:

#include <stdlib.h>
int foo(void) {
  _Ptr<void (void *)> p = _Assume_bounds_cast<_Ptr<void (void *)>>(NULL);
  return 0;
}

Trying to compile results in error:
clang -c foo.c --

3:27: error: can only cast function names or null pointers to checked function pointer type '_Ptr<void (void *)>'
  _Ptr<void (void *)> p = _Assume_bounds_cast<_Ptr<void (void *)>>(NULL);
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.