Add build-montauk-toolchain.sh: builds an OS-aware cross GCC/binutils
(same versions and prefix as the bare-metal x86_64-elf toolchain) whose
x86_64-montauk target links static ET_EXEC binaries against the Montauk
libc sysroot with no special flags: 4 KiB max page size for the kernel
ELF loader, -mno-red-zone by default, crt1/crti/crtn + -lc from the
sysroot, __montauk__ defined. Target patches are checked into
toolchain/patches/, the GCC target header into toolchain/files/.
sys/types.h now includes <stdint.h> so hosted code (libgcov and
friends) sees intptr_t via the stdio include chain.
Co-Authored-By: Claude Fable 5 <[email protected]>