Added ErrorOr-returning syscall wrappers for mmap, munmap, mprotect, and pkey_mprotect in src/__support/OSUtil/linux/syscall_wrappers/. Migrated the sys/mman Linux entrypoint implementations to use them, following the design in libc/docs/dev/syscall_wrapper_refactor.rst. Removed the shared mprotect_common.h in favour of per-syscall wrapper headers. Added hdr/sys_mman_macros.h proxy header.