Casting bool to pointer type results in invalid Rust

[jorendorff]

The fix should be the same as #1030, but presumably with something like size_t as the intermediate type.

(Why, you might ask, would anyone ever do this in real code. The answer is that C doesn't have generics, so projects will have, say, a single hash table type with void * values, and store booleans in it by casting.)

[fw-immunant]

This code reproduces this bug:

#include <stdbool.h>

void f(bool b) {
    void* x = (void*)b;
}

It gets translated to:

#[no_mangle]
pub unsafe extern "C" fn f(mut b: bool) {
    let mut x: *mut libc::c_void = b as *mut libc::c_void;
}

which does not compile (E0606).