feat: POSIX libc surface, native binutils (as/ld/ar run on MontaukOS)

Grow the Montauk libc enough to cross-build binutils 2.43.1 with
--host=x86_64-montauk. gas, ld, ar, nm, objcopy, objdump, readelf,
ranlib, strip and friends now link as native ET_EXEC Montauk binaries
(staged stripped in toolchain/native/, not yet shipped in the image).

New libc surface: full Linux errno and signal sets, O_* flags with
real O_EXCL/O_APPEND semantics, unlink/rmdir/dup/dup2/getpid/_exit,
kill (SYS_KILL), fcntl, fileno/fdopen, putc/getchar/rewind,
ctime/asctime, strtoll/strtoull/atoll, bsearch, mkstemp/mktemp,
realpath (lexical, drive-prefix aware), mbstowcs/mblen, chmod/fchmod/
umask/utime no-ops (VFS has no modes or settable times), full struct
stat with fake inodes, sscanf field widths (bounded conversions),
SCN*/PRI* completions, wait/waitpid over SYS_WAITPID, and new headers
sys/wait.h, sys/param.h, utime.h, wchar.h, memory.h.

fork/exec/pipe are declared but fail with ENOSYS: binutils never
spawns, and real process plumbing is the posix_spawn milestone, which
needs kernel support (exit status reporting, fd redirection).

TCC's montauk_compat.h shims (unlink, chmod, execvp, realpath, fdopen,
strtoll, strtoull) are retired in favor of the libc versions.

Co-Authored-By: Claude Fable 5 <[email protected]>

programs/include/libc/sys/wait.h

@@ -0,0 +1,31 @@
+#ifndef _LIBC_SYS_WAIT_H
+#define _LIBC_SYS_WAIT_H
+
+#pragma once
+
+#include <sys/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Status decoding. The Montauk kernel does not yet report exit codes
+   through SYS_WAITPID, so waited children always decode as exit 0. */
+#define WIFEXITED(s)    (((s) & 0x7F) == 0)
+#define WEXITSTATUS(s)  (((s) >> 8) & 0xFF)
+#define WIFSIGNALED(s)  (0)
+#define WTERMSIG(s)     (0)
+#define WIFSTOPPED(s)   (0)
+#define WSTOPSIG(s)     (0)
+
+#define WNOHANG   1
+#define WUNTRACED 2
+
+pid_t wait(int *status);
+pid_t waitpid(pid_t pid, int *status, int options);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _LIBC_SYS_WAIT_H */