LinxV5: emit ELF machine 0xE9

[zhoubot]

Summary

• change LinxV5 ELF e_machine from legacy 0x105 to the current LinxISA ABI value 0xE9
• add MC/linker regression coverage for relocatable objects and executables

Closes #76.

Validation

• fresh Release+assertions build of clang, lld, llvm-mc, llvm-readobj, and llvm-objdump
• MC object header: EM_LinxV5 (0xE9)
• lld executable header: EM_LinxV5 (0xE9)
• clang integrated assembler/linker executable header: EM_LinxV5 (0xE9)
• targeted FileCheck RUN lines pass

Integration gate

This PR stays draft until the SuperNPUBench corpus is rebuilt with this exact commit and the full promoted ASL model suite passes result-data validation.

[zhoubot]

Added commit f7b19f6 to close the PTO relative-generation Matrix path:

• Matrix pseudo sources now remain T#/U#/M#/N# relative selectors and the destination is an ordinary Local Tile (U in the regression), not the retired ACC register class.
• Multi-packet B.IOT emission preserves source order and places the destination on the terminating packet.
• Mixed-type Matrix B.DATR now encodes PadValue=Zero.
• Added the B.DATR dtype, Zero, RNONE, NOSAT assembler alias required by TileOP API.

Evidence: 5 focused MC/CodeGen tests pass; Clang integrated assembler produces an object whose disassembly preserves exact relative source order and ->u<64KB>; no MC printer crash.