cc -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations uchar/c16rtomb.c -o uchar/c16rtomb -D_POSIX_C_SOURCE=202405L  -lm -lpthread  -liconv
uchar/c16rtomb.c:1:10: fatal error: 'uchar.h' file not found
    1 | #include <uchar.h>
      |          ^~~~~~~~~
1 error generated.