self-hosted: refactor some code out of Module.zig into zir_sema.zig

This makes sense from an organizational point of view, as explained by
this new doc comment at the top of the new file:

//! Semantic analysis of ZIR instructions.
//! This file operates on a `Module` instance, transforming untyped ZIR
//! instructions into semantically-analyzed IR instructions. It does type
//! checking, comptime control flow, and safety-check generation. This is the
//! the heart of the Zig compiler.
//! When deciding if something goes into this file or into Module, here is a
//! guiding principle: if it has to do with (untyped) ZIR instructions, it goes
//! here. If the analysis operates on typed IR instructions, it goes in Module.

Before:
   4009 src-self-hosted/Module.zig

After:
   2776 src-self-hosted/Module.zig
   1128 src-self-hosted/zir_sema.zig

This should be sufficient to avoid the situation we have in stage1 where
ir.cpp is 32,516 lines.

0 files changed, 0 insertions, 0 deletions