Ports: Add zig port

[sin-ack]

Shoutouts to IdanHo for the flock ideas, Daniel for various syscall implementations, and timschumi for the awesome LibC work.

Yak stack:

• [x] Do not hardcode constants in serenity.zig. Instead, bundle a generate-serenity-constants.zig file with the port, and use that to generate constant values during the build by importing LibC headers from Zig.
• [x] Symlink the appropriate LLVM patches from Toolchain/LLVM instead of bundling them. This can't be done for the libcxx patch as it needs to be adapted for Zig.
• [ ] (Optional) Figure out how to properly let go of the TLS segment of the program during execve so that zig run works.

[sin-ack]

Need to fix PTHREAD_STACK_MAX being needed by LibELF in Lagom.