Enable assembly for x86-64

[randomPoison]

The original c2rust transpile of dav1d disabled assembly support in the meson configuration options (-Denable_asm=false). To start getting assembly integrated into the Rust port we should start by getting x86_64 assembly enabled, built, and linked.

To re-transpile with assembly enabled, follow the steps in this comment but in the meson configure step, change enable_asm=false to enable_asm=true.

The build.rs will need to be setup to compile the appropriate source files using NASM and link the build output. Check out the build.rs in the rav1e project for an example of how a similar project is doing this using the nasm-rs crate.