Fix compilation on Zig master

[AnErrupTion]

This PR fixes compilation on Zig master by changing the following:

• @XToY() to @YFromX(), as well as adding separate calls to @as() to coerce to the correct type (this was run by zig fmt).
• The @breakpoint() function (used in MicroZig) now, at least on this specific platform, requires a publicly-exported abort() function, which wasn't present. I've added a simple abort function.

Additionally, I've removed the LLVM issue warning in the README.md, because, at least, it works fine for me with the latest Zig compiler (when the project is built in Debug mode, as described).

[dxxb]

Thank you for pushing this PR. I came here to push an equivalent fix but you beat me to it 😄
Additionally I found I cannot compile the blinky example code because GPIO and Pin abstractions need fixing too.

[AnErrupTion]

@dxxb Yeah, I found this out after opening the PR. It'll require more work, but I'm unsure if I should do it in this PR directly, or in a separate one.