Use bindgen in build.rs

[nixpulvis]

I'm looking into possibly using this crate for alacritty/alacritty#4299, and during my read over of the code I was a bit surprised to see the generated.rs file was a fixed output from bindgen. I've added bindgen as a build dependency and updated the build.rs file accordingly.

The main thing I was confused about during the process was the note in the build.sh script:

Do note that macOS 10.9 (Mavericks) SDK MUST be used for code generation

in conjunction with the line:

  -IMacOSX-SDKs/MacOSX10.13.sdk/usr/include

However, it seems that this does in fact work, at least for the one system call I tested directly.

[svartalf]

Hi, @nixpulvis! Yes, using bindgen directly sounds like a better solution, I used pre-generated bindings file only for two reasons:

1. I don't have macOS on hand and cross-compilation does not really works because of missing headers on Linux (unless you download them from somewhere, etc, etc, you know the drill)
2. As darwin-libproc is at the moment used only by me, I was not spending much time on its quality or functionality coverage as long as it's good enough for being used in heim crate.

I agree that fixing all these small quirks and stabilizing it in a nearest future would be great; I'll try to check your PR a bit later today!