Fix mixed signed / unsigned types

Add NVPTX architecture

change c_{,u}long to match libc v0.2.23 definitions

add MSP430 support

Copied a few extra definitions from the libc crate.

Include additional types from libc

Copied a few extra definitions from the libc crate.

11: Re-export core::ffi::c_void r=japaric a=jeikabu

japaric/cty#10

Without this trying to use bindgen like:
```rust
let bindings = bindgen::Builder::default()
        .header("wrapper.h")
        .ctypes_prefix("cty")
        .use_core()
        .generate();
```

Results in lots of:
```
error[E0308]: mismatched types
  --> runng/src/protocol/mod.rs:49:43
   |
49 |         let res = nng_setopt(socket, opt, topic_ptr, topic_size);
   |                                           ^^^^^^^^^ expected enum `cty::c_void`, found enum `std::ffi::c_void`
   |
   = note: expected type `*const cty::c_void`
              found type `*const std::ffi::c_void`
```


Co-authored-by: jake <jeikabu@gmail.com>

v0.2.0