fix cross-compile datalayout

[cs01]

Summary

• Fixed chad build --target linux-x64 failing with unknown specifier 'x' target datalayout = "x86_64-unknown-linux-gnu" — the native binary was emitting the target triple as the LLVM data layout string
• Root cause: native-compiler-lib.ts typed targetInfo as any to avoid importing TargetInfo from target.ts (which depends on Node's os module). The native compiler couldn't resolve GEP field indices for the any-typed object, so this.targetInfo.dataLayout read the wrong struct field (returning the triple instead)
• Fix: extracted TargetInfo interface and LibC type into a new dependency-free src/target-types.ts, allowing the self-hosted path to import proper type info without pulling in Node's os module
• Strengthened cross-compilation tests: datalayout assertion now validates actual content (must start with e-, not be the triple), and added a native binary cross-compile test that would have caught this bug in CI

Test plan

• npm test — 226 tests pass (225 existing + 1 new native binary cross-compile test)
• npm run verify:quick — self-hosting verification passed (Stage 0 + Stage 1)
• .build/chad ir --target linux-x64 now emits correct target datalayout = "e-m:e-p270:32:32-..." instead of the triple
• Node.js path (node dist/chad-node.js build --target linux-x64) still works