branches: 1.1.2; 1.1.6;
libc: New C11 functions mbrtoc16, mbrtoc32, c16rtomb, c32rtomb.

The mbrtoc16/32 functions read mulitbyte strings according to the
current locale into UTF-16/32 code unit sequences; the c16/32rtomb
functions write UTF-16/32 code unit sequences into multibyte strings
according to the current locale. The `r' means restartable: they
work incrementally and pick up where they left off.

NOTE: This bumps the libc minor version, since it adds new symbols.

PR lib/52374: <uchar.h> missing