I'm allowing incremental compilation of ZIR modules to be broken. This
is not a real use case of ZIR, and the feature requires a lot of code
duplication with incremental compilation of Zig AST (which works great).
* anonymous decls have automatically generated names and symbols, and
participate in the same memory management as named decls.
* the Ref instruction is deleted
* the DeclRef instruction now takes a `[]const u8` and DeclRefStr takes
an arbitrary string instruction operand.
* introduce a `zir.Decl` type for ZIR Module decls which holds
content_hash and name - fields that are not needed for `zir.Inst`
which are created as part of semantic analysis. This improves the
function signatures of Module.zig and lowers memory usage.
* the Str instruction is now defined to create an anonymous Decl and
reference it.
* Take advantage of coercing anonymous struct literals to struct types.
* Reworks Module to favor Zig source as the primary use case.
Breaks ZIR compilation, which will have to be restored in a future commit.
* Decl uses src_index rather then src, pointing to an AST Decl node
index, or ZIR Module Decl index, rather than a byte offset.
* ZIR instructions have an `analyzed_inst` field instead of Module
having a hash table.
* Module.Fn loses the `fn_type` field since it is redundant with
its `owner_decl` `TypedValue` type.
* Implement Type and Value copying. A ZIR Const instruction's TypedValue
is copied to the Decl arena during analysis, which allows freeing the
ZIR text instructions post-analysis.
* Don't flush the ELF file if there are compilation errors.
* Function return types allow arbitrarily complex expressions.
* AST->ZIR for function calls and return statements.
* Introduce the concept of anonymous Decls
* Primitive Hello, World with inline asm works
* There is still an unsolved problem of how to manage ZIR instructions
memory when generating from AST. Currently it leaks.
