* m4/uchar_h.m4 (gl_UCHAR_H, gl_TYPE_CHAR8_T, gl_TYPE_CHAR16_T,
gl_TYPE_CHAR32_T): Before including <uchar.h>, on Haiku, first include
<stdint.h>.
* m4/c32rtomb.m4 (gl_FUNC_C32RTOMB): Likewise.
* m4/mbrtoc32.m4 (gl_FUNC_MBRTOC32, gl_CHECK_FUNC_MBRTOC32,
gl_MBRTOC32_EMPTY_INPUT, gl_MBRTOC32_C_LOCALE, gl_MBRTOC32_SANITYCHECK):
Likewise.
* lib/uchar.in.h: On Haiku, include <stdint.h> before the include_next.
* doc/posix-headers/uchar.texi: Mention the Haiku bug.