feat: native GCC - cc1, cc1plus and the gcc driver run on MontaukOS

Cross-build GCC 14.2.0 with --host=x86_64-montauk: the driver, cc1,
cc1plus and collect2 now link as static Montauk ET_EXEC binaries
against the hosted libstdc++, and ship in the SDK. Together with the
native binutils, TCC and the target sysroot, MontaukOS carries a
complete self-contained C and C++ toolchain at 0:/sdk.

libc: anonymous mmap/munmap over SYS_ALLOC (GCC's page allocator
wants mmap; SYS_ALLOC memory is page-aligned by construction),
getpagesize, minimal sysconf, MB_CUR_MAX, isascii/toascii, POSIX id
typedefs (ino_t, dev_t, nlink_t, ...), struct stat fields switched to
proper POSIX types (st_size is a signed off_t now), and a
conventional _STDIO_H guard marker so GMP's FILE detection works.

Build recipe and the five host-build gotchas (bundled config.subs,
gettext removal, stdio guard sniffing, endianness cache preset,
sysroot sdk symlink) are documented in toolchain/README.md. The
devkit stages the driver as gcc.elf/g++.elf/cpp.elf, the backends in
the libexec layout the driver expects, a copy of ld where collect2
searches, and a 0:/tmp scratch dir. Ramdisk: 1604 files, 368 MB.

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

programs/lib/libc/libc.c

@@ -22,6 +22,7 @@
 #include <sys/stat.h>
 #include <utime.h>
 #include <spawn.h>
+#include <sys/mman.h>
 #include <sys/time.h>
 #include <unistd.h>
 
@@ -2286,7 +2287,7 @@ int stat(const char *path, struct stat *buf) {
     int h = (int)_zos_syscall1(SYS_OPEN, (long)path);
     if (h >= 0) {
         buf->st_mode = S_IFREG;
-        buf->st_size = (unsigned long)_zos_syscall1(SYS_GETSIZE, (long)h);
+        buf->st_size = (off_t)_zos_syscall1(SYS_GETSIZE, (long)h);
         _zos_syscall1(SYS_CLOSE, (long)h);
         /* No inodes in the VFS API: derive a stable id from the path
            so that distinct paths compare as distinct files. */
@@ -2297,7 +2298,7 @@ int stat(const char *path, struct stat *buf) {
         buf->st_ino = ino | 1;
         buf->st_nlink = 1;
         buf->st_blksize = 4096;
-        buf->st_blocks = (buf->st_size + 511) / 512;
+        buf->st_blocks = (blkcnt_t)((buf->st_size + 511) / 512);
         return 0;
     }
 
@@ -2318,13 +2319,13 @@ int fstat(int fd, struct stat *buf) {
     }
     memset(buf, 0, sizeof(*buf));
     buf->st_mode = S_IFREG;
-    buf->st_size = (unsigned long)_zos_syscall1(SYS_GETSIZE, (long)fd);
+    buf->st_size = (off_t)_zos_syscall1(SYS_GETSIZE, (long)fd);
     /* Handles do not map back to paths, so fake a per-handle inode in a
        range disjoint from the path hashes used by stat(). */
     buf->st_ino = 0x4000000000000000UL + (unsigned long)fd;
     buf->st_nlink = 1;
     buf->st_blksize = 4096;
-    buf->st_blocks = (buf->st_size + 511) / 512;
+    buf->st_blocks = (blkcnt_t)((buf->st_size + 511) / 512);
     return 0;
 }
 
@@ -3711,6 +3712,57 @@ int kill(pid_t pid, int sig) {
     return 0;
 }
 
+int getpagesize(void) {
+    return 4096;
+}
+
+long sysconf(int name) {
+    switch (name) {
+    case 4:    /* _SC_OPEN_MAX */
+        return 64;
+    case 30:   /* _SC_PAGESIZE */
+        return 4096;
+    case 84:   /* _SC_NPROCESSORS_ONLN */
+        return 1;
+    default:
+        errno = EINVAL;
+        return -1;
+    }
+}
+
+/* Anonymous mappings only: SYS_ALLOC hands back zeroed page-aligned
+   memory and SYS_FREE releases it. Length is remembered by the kernel
+   per allocation, so munmap ignores its length argument. */
+void *mmap(void *addr, size_t length, int prot, int flags, int fd,
+           long offset) {
+    (void)addr; (void)prot; (void)offset;
+    if (length == 0 || fd != -1 || !(flags & MAP_ANONYMOUS)) {
+        errno = ENODEV;
+        return MAP_FAILED;
+    }
+    void *p = (void *)_zos_syscall1(SYS_ALLOC, (long)length);
+    if (p == NULL) {
+        errno = ENOMEM;
+        return MAP_FAILED;
+    }
+    return p;
+}
+
+int munmap(void *addr, size_t length) {
+    (void)length;
+    if (addr == NULL || addr == MAP_FAILED) {
+        errno = EINVAL;
+        return -1;
+    }
+    _zos_syscall1(SYS_FREE, (long)addr);
+    return 0;
+}
+
+int mprotect(void *addr, size_t length, int prot) {
+    (void)addr; (void)length; (void)prot;
+    return 0;   /* page protections are not adjustable from userspace */
+}
+
 long pathconf(const char *path, int name) {
     (void)path;
     switch (name) {