This patch adds comprehensive assembler (MC layer) support for the
Mach-O object file format on RISC-V targets, enabling assembly and
disassembly of RISC-V code targeting Apple platforms.
Key changes:
- Define RISC-V-specific Mach-O relocation types in BinaryFormat/MachO.h
- Implement RISCVMachObjectWriter with full relocation handling for:
- PCREL_HI/LO pairs for PC-relative addressing
- GOT relocations for external symbols
- Branch relocations (CALL, unconditional/conditional branches)
- Data section relocations
Test files include llvm-otool dumps to verify the generated relocations.
This code is based on code originally written by Tim Northover.
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