LLVM Backend Experimental (176)

Objective: offer an optional advanced LLVM backend.

Surface backend

• backend selectable: llvm-exp
• preserves profiles (enterprise-*) and optimization options
• respects the LLVM toolchain (IR -> object -> link)

Foundation Capabilities

• LLVM IR emission (via backend bindings)
• debug metadata path (via profile options)
• optimization bridge (O0..Oz, LTO/PGO compat checks)
• target lowering multi-target (x86_64, aarch64, riscv64, i386)
• linker integration via toolchain status/diagnostics

Pipeline security contract

• on failure object/toolchain: explicit codegen error
• no silent fallback on critical backend
• diagnostics reduced to driver level