x86_64-managarm-gcc -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations threads/once_flag.c -o threads/once_flag -D_POSIX_C_SOURCE=202405L -lm -lpthread -lrt -lintl -liconv
threads/once_flag.c:2:1: error: unknown type name ‘once_flag’
    2 | once_flag* foo;
      | ^~~~~~~~~