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/errno.h

@@ -9,18 +9,48 @@ extern "C" {
 
 extern int errno;
 
-#define ENOENT  2
-#define EIO     5
-#define ENOMEM  12
-#define EACCES  13
-#define EINVAL  22
-#define ERANGE  34
-#define ENOSYS  38
-#define EISDIR  21
-#define ENOTDIR 20
-#define EEXIST  17
-#define EBADF   9
-#define EPERM   1
+/* Linux errno numbering. */
+#define EPERM        1
+#define ENOENT       2
+#define ESRCH        3
+#define EINTR        4
+#define EIO          5
+#define ENXIO        6
+#define E2BIG        7
+#define ENOEXEC      8
+#define EBADF        9
+#define ECHILD       10
+#define EAGAIN       11
+#define ENOMEM       12
+#define EACCES       13
+#define EFAULT       14
+#define EBUSY        16
+#define EEXIST       17
+#define EXDEV        18
+#define ENODEV       19
+#define ENOTDIR      20
+#define EISDIR       21
+#define EINVAL       22
+#define ENFILE       23
+#define EMFILE       24
+#define ENOTTY       25
+#define EFBIG        27
+#define ENOSPC       28
+#define ESPIPE       29
+#define EROFS        30
+#define EMLINK       31
+#define EPIPE        32
+#define EDOM         33
+#define ERANGE       34
+#define EDEADLK      35
+#define ENAMETOOLONG 36
+#define ENOLCK       37
+#define ENOSYS       38
+#define ENOTEMPTY    39
+#define ELOOP        40
+#define EWOULDBLOCK  EAGAIN
+#define EOVERFLOW    75
+#define ETIMEDOUT    110
 
 #ifdef __cplusplus
 }