Functions called in checked scope must have prototype

[john-h-kastner]

Any functions called from inside a _Checked scope must have a prototype. For example in the following code foo does not have a prototype, but it is called in a function that could otherwise be made _Checked.

int foo() {
  return 0;
}

int bar() {
  return foo();
}

Conversion (-addcr):

int foo() _Checked {
  return 0;
}

int bar() _Checked {
  return foo();
}

This conversion is rejected by clang with error: function without a prototype cannot be used or declared in a checked scope. For this conversion to work, we need to rewrite foo as int foo(void) _Checked. We already add void prototypes while rewriting function definitions, so we should be able to apply this code to add the same prototype on functions called from checked scopes.