In-place binary/jit updating

Loris Cro and Andrew Kelley recently published a blog post (https://kristoff.it/blog/zig-new-relationship-llvm/) about Ziglang's new self-hosted compiler. Part of the post is about how they can do in-place patching of the binary to avoid doing linking when changing small amounts of code (or maybe larger amounts too, I'm not sure). This seems extremely powerful. Linking is consistently a significant bottleneck in compiling rust, and completely skipping it would probably result in crazy speedups for compiling.

I'm proposing that this project pursue this either in a similar way to Zig, by patching individual functions in the output binary, or by keeping the jit open and recompiling individual functions as the source changes.

Start by reading the linked Zig self-hosted compiler blog post and compare its in-place binary patching approach with the project's current compilation and linking flow. The issue does not name files, tests, or an entry point, and completion would require defining whether function patching or keeping a JIT open is the intended design.