This non-standard type type is unused in the base system (__ct_rune_t or
__rune_t are used instead) and ports. It has been around as long as our
current source repo, but we have avoided using it. In sys/_types.h
where the __*rune_t typedefs are defined, the following appears in a
comment:
NOTE: rune_t is not covered by ANSI nor other standards, and should
not be instantiated outside of lib/libc/locale. Use wchar_t.
The definition of this unused type meant we gratutiously differed from
standards compliant stddef.h/stdlib.h.
PR: 279357 (exp-run by antoine)