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/src/tcc/montauk_compat.h

@@ -2,83 +2,20 @@
     * montauk_compat.h
     * POSIX compatibility shims for TCC on MontaukOS
     * Copyright (c) 2026 Daniel Hammer
+    *
+    * Historical note: this header used to carry static fallbacks for
+    * unlink/chmod/execvp/realpath/fdopen before the Montauk libc grew
+    * them (native binutils port). It is now a thin passthrough.
 */
 
 #ifndef MONTAUK_COMPAT_H
 #define MONTAUK_COMPAT_H
 
-#include <stddef.h>
-#include <stdint.h>
-
-/* getcwd is provided by libc now */
-char *getcwd(char *buf, size_t size);
-
-/* chmod - no-op on MontaukOS */
-static inline int chmod(const char *path, unsigned int mode) {
-    (void)path; (void)mode;
-    return 0;
-}
-
-/* close (provided by libc) */
-int close(int fd);
-
-/* lseek - provided by libc, tracks fd positions */
-long lseek(int fd, long offset, int whence);
-
-/* realpath - just return a copy of the path */
-static inline char *realpath(const char *path, char *resolved) {
-    if (path == NULL) return NULL;
-    if (resolved == NULL) {
-        size_t len = 0;
-        const char *p = path;
-        while (*p++) len++;
-        resolved = (char*)malloc(len + 1);
-        if (!resolved) return NULL;
-    }
-    {
-        const char *s = path;
-        char *d = resolved;
-        while ((*d++ = *s++));
-    }
-    return resolved;
-}
-
-/* dlfcn stubs not needed -- TCC_IS_NATIVE is disabled for MontaukOS */
-
-/* ====================================================================
-   ssize_t (used in tccelf.c)
-   ==================================================================== */
-
-#ifndef _SSIZE_T_DEFINED
-#define _SSIZE_T_DEFINED
-typedef long ssize_t;
-#endif
-
-/* ====================================================================
-   POSIX I/O (provided by libc)
-   ==================================================================== */
-
-int read(int fd, void *buf, size_t count);
-int write(int fd, const void *buf, size_t count);
-
-/* unlink = remove */
-static inline int unlink(const char *path) {
-    return remove(path);
-}
-
-/* fdopen - MontaukOS doesn't have fd-to-FILE conversion.
-   TCC uses fdopen after creating a file with open().
-   We return NULL and let TCC fall back to error path,
-   or we can use a workaround. */
-FILE *fdopen(int fd, const char *mode);
-
-/* ====================================================================
-   Process stubs
-   ==================================================================== */
-
-static inline int execvp(const char *file, char *const argv[]) {
-    (void)file; (void)argv;
-    return -1;
-}
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 
 #endif /* MONTAUK_COMPAT_H */