nix 0.30.1 expects SaFlags_t = c_ulong for target_os = "redox"
(see nix-0.30.1/src/sys/signal.rs:430). Our relibc had c_int,
causing type mismatch errors in uutils and any nix-dependent crate.
Align with nix's expectation.
inttypes.h included wchar.h for wchar_t and stdint.h, but this created
a circular dependency: wchar.h → stdint.h → gnulib inttypes.h →
inttypes.h → wchar.h. When gnulib's wchar.h wrapper was re-entered
during this cycle, wint_t and mbstate_t were not yet defined.
POSIX spec says inttypes.h should include stdint.h directly and
wchar_t comes from stddef.h. Using stdint.h + stddef.h breaks the
circular chain at its source.
relibc's wchar.h included <stdio.h> before defining wint_t and
mbstate_t. The circular chain wchar.h → stdio.h → inttypes.h →
wchar.h caused gnulib's wchar.h wrapper (used by m4, bison, etc.)
to see 'unknown type name wint_t' and 'unknown type name mbstate_t'.
Fix: Move stdio.h and time.h from sys_includes (which cbindgen
emits before type definitions) into after_includes, after wchar_t,
wint_t, and mbstate_t are defined. Also define mbstate_t manually
in after_includes with a guard, and exclude it from cbindgen export
to prevent duplicate definitions.