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/include/libc/stdlib.h

@@ -62,6 +62,8 @@ int                mkstemp(char *template_);
 char              *mktemp(char *template_);
 char              *realpath(const char *path, char *resolved);
 size_t             mbstowcs(wchar_t *dst, const char *src, size_t n);
+#define MB_CUR_MAX 1
+
 int                mblen(const char *s, size_t n);
 int                mbtowc(wchar_t *pwc, const char *s, size_t n);
 int                wctomb(char *s, wchar_t wc);