macOS platform bindings: Syscall.rux, Platform.rux, and smoke test

[devsker]

Summary

Implements the macOS platform bindings for Rux, providing both a low-level raw syscall FFI module (MacOS) and a Platform module that fulfills the Std library contract.

Changes

Src/Syscall.rux — Raw macOS syscall FFI:

• Syscall constants using the BSD class mask (0x2000000 | number): SYS_READ, SYS_WRITE, SYS_CLOSE, SYS_MMAP, SYS_MUNMAP, SYS_EXIT, SYS_GETPID
• macOS-specific mmap flags (MAP_PRIVATE = 0x0002, MAP_ANONYMOUS = 0x1000)
• extern block via @[Import(lib: "rux-macos")] consuming the __rux_macos_syscall* thunks added in Add __rux_macos_syscall thunks for raw macOS syscall access Rux#182
• Typed wrappers: Read, Write, Close, Exit, GetPid, Mmap, Munmap, Syscall0–Syscall6, IsError, Errno

Src/Platform.rux — Std library contract implementation:

• PlatformAlloc/Realloc/Free — mmap-based allocator with 8-byte header tracking
• PlatformCopy/Fill/Zero/Compare — byte-level utilities
• PlatformReadStdin/PlatformWriteStdout/PlatformWriteStdoutWide — I/O primitives
• PlatformExit — process termination

Examples/Smoke/ — Smoke test exercising Read, Write, GetPid, Mmap, and Munmap (exit code 0 on success).

Notes

• x86-64 only — the Mach-O linker currently emits only x86-64 machine code. Apple Silicon support is blocked on the compiler side.
• nanosleep and clock_gettime are intentionally omitted — on macOS these are implemented in libSystem, not as raw kernel traps, so they cannot be exposed through this raw syscall interface.
• The pub keyword on struct fields is parsed but cross-module field access is not yet fully resolved in the compiler, so Timespec helpers were removed from the API surface.

Related

Depends on rux-lang/Rux#182 which adds the __rux_macos_syscall* linker thunks.