Move the LLVM type-mapping and C-ABI coercion helpers out of emit_llvm.zig into
the first src/backend/llvm/ modules. Behavior-preserving relocation — the only
rewrites are module plumbing and self.* -> self.e.* facade access.
- src/backend/llvm/types.zig (TypeLowering): toLLVMType + toLLVMTypeInfo.
- src/backend/llvm/abi.zig (AbiLowering): abiCoerceParamType / abiCoerceParamTypeEx
/ needsByval / materializeByvalArg.
- Both are backend *LLVMEmitter facades (field `e`) — the backend analogue of the
IR-side *Lowering facades, NOT a *Lowering facade. They reach the cached LLVM
handles, IR type table, module data layout, builder, and the memoizing
composite-type getters via self.e.*.
- LLVMEmitter stays the facade: toLLVMType (~97 callers) + abiCoerceParamType /
abiCoerceParamTypeEx / needsByval / materializeByvalArg kept as thin wrappers
delegating through new typeLowering()/abiLowering() accessors. Zero caller
churn. toLLVMTypeInfo deleted (sole caller moved).
- Widened getStringStructType / getAnyStructType / getClosureStructType to pub
(the moved toLLVMTypeInfo calls them back; their memoization stays on
LLVMEmitter). verifySizes stays in emit_llvm.zig (size-assertion pass, not type/
ABI lowering). No ABI/type logic, branch order, diagnostic text, or snapshot
changed. Circular import (emit_llvm <-> backend/llvm) resolves via the pointer
facade.
Gate: zig build, zig build test, bash tests/run_examples.sh -> 361/0
(1202 .ir + the 2 ABI unit tests unchanged, no churn).
