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 <noreply@anthropic.com>

programs/include/libc/sys/param.h

@@ -0,0 +1,23 @@
+#ifndef _LIBC_SYS_PARAM_H
+#define _LIBC_SYS_PARAM_H
+
+#pragma once
+
+#include <limits.h>
+#include <sys/types.h>
+
+#ifndef MAXPATHLEN
+#define MAXPATHLEN 4096
+#endif
+
+#ifndef MIN
+#define MIN(a, b) (((a) < (b)) ? (a) : (b))
+#endif
+#ifndef MAX
+#define MAX(a, b) (((a) > (b)) ? (a) : (b))
+#endif
+
+#define howmany(x, y) (((x) + ((y) - 1)) / (y))
+#define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))
+
+#endif /* _LIBC_SYS_PARAM_H */

programs/include/libc/sys/stat.h

@@ -12,19 +12,54 @@ extern "C" {
 #define S_IFMT  0170000
 #define S_IFDIR 0040000
 #define S_IFREG 0100000
+#define S_IFCHR 0020000
+#define S_IFLNK 0120000
 
-#define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
-#define S_ISREG(mode) (((mode) & S_IFMT) == S_IFREG)
+#define S_ISDIR(mode)  (((mode) & S_IFMT) == S_IFDIR)
+#define S_ISREG(mode)  (((mode) & S_IFMT) == S_IFREG)
+#define S_ISCHR(mode)  (((mode) & S_IFMT) == S_IFCHR)
+#define S_ISLNK(mode)  (((mode) & S_IFMT) == S_IFLNK)
+#define S_ISFIFO(mode) (0)
+#define S_ISSOCK(mode) (0)
+#define S_ISBLK(mode)  (0)
+
+/* Permission bits are accepted and preserved by the API for POSIX
+   compatibility, but the Montauk VFS does not store them. */
+#define S_IRWXU 0700
+#define S_IRUSR 0400
+#define S_IWUSR 0200
+#define S_IXUSR 0100
+#define S_IRWXG 0070
+#define S_IRGRP 0040
+#define S_IWGRP 0020
+#define S_IXGRP 0010
+#define S_IRWXO 0007
+#define S_IROTH 0004
+#define S_IWOTH 0002
+#define S_IXOTH 0001
 
 struct stat {
+    unsigned long st_dev;
+    unsigned long st_ino;
     mode_t        st_mode;
+    unsigned long st_nlink;
+    uid_t         st_uid;
+    gid_t         st_gid;
     unsigned long st_size;
+    unsigned long st_blksize;
+    unsigned long st_blocks;
+    time_t        st_atime;
     time_t        st_mtime;
+    time_t        st_ctime;
 };
 
-int mkdir(const char *path, unsigned int mode);
-int stat(const char *path, struct stat *buf);
-int fstat(int fd, struct stat *buf);
+int    mkdir(const char *path, unsigned int mode);
+int    stat(const char *path, struct stat *buf);
+int    fstat(int fd, struct stat *buf);
+int    lstat(const char *path, struct stat *buf);
+int    chmod(const char *path, mode_t mode);
+int    fchmod(int fd, mode_t mode);
+mode_t umask(mode_t mask);
 
 #ifdef __cplusplus
 }

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 */