Native split codegen cannot materialize relocatable ptrtoint constant operands

[proggeramlug]

Summary

The split native codegen-unit path cannot materialize the relocatable
ptrtoint constant expression that every non-entry JS module uses to pass its
__init_body function pointer through the integer-valued runtime ABI.

This blocks production-sized webpack graphs before application code can run.
The whole-module text path accepts the same IR because LLVM parses the constant
expression itself; the in-process native dialect reader instead feeds the full
expression to the integer literal parser.

Exact reproduction

Base: fe0d4979204dfd6b8b166320e1ebdd2318f30518 (current main after #8044)

Using the pinned Next.js 16.3.0 webpack production route graph from #8034,
compiled as an app-only dylib with native split units:

perry compile --no-cache --no-auto-optimize --output-type dylib perry-host.js -o next-app-route.dylib

Perry collects 91 modules and reaches native codegen, then independently fails
all four large split modules, including the generated
next/dist/compiled/next-server/app-route.runtime.prod.js:

native codegen unit ... failed: ...
bad integer `ptrtoint (ptr @<module-prefix>__init_body to i64)`

Perry correctly refuses to link the incomplete dylib (87/91 modules emitted).

Minimal compiler-level reproduction

Define two functions in an LlModule: an __init_body, and an __init wrapper
whose runtime call uses this operand:

i64 ptrtoint (ptr @fixture_js__init_body to i64)

Then invoke compile_module_units_native(..., 2, ...). This forces independent
native construction and object emission followed by the real partial-link path.
Before the fix it reaches i128::parse and fails with bad integer; a parse-only
or textual-backend test does not reproduce the defect.

Acceptance

• The focused two-unit emitted-object/link regression passes.
• The exact production graph gets past these four ptrtoint construction
  failures.
• No [Next.js/dylib] Add a pinned production App Route parity fixture and CI gate #8034 behavior acceptance is inferred: its generated
  AppRouteRouteModule.handle path must still actually execute with the required
  moving/verifier evidence before that separate production ticket can close.

Refs #8034 and #8040.

[proggeramlug]

Verified on PR #8058 head 2dd16ae88fe22593babad15c78d8a9c086dfba0f against the exact cold 91-module Next.js 16.3.0 production replay. All four former failures cleared native construction, object emission, and partial link: webpack chunk 2.js 3/3 units -> 7.2 MiB; jsonwebtoken 2/2 -> 5.0 MiB; App Page runtime 12/12 -> 31.3 MiB; App Route runtime 4/4 -> 9.7 MiB. The graph continued into later modules with no bad integer ptrtoint (...) failure. This proves #8057 only; route execution and moving/verifier acceptance remain open under #8034/#8040.