/opt/IBM/openxlC/17.1.1/bin/ibm-clang -pthread   -Wall -Wextra -Werror=implicit-function-declaration utf8-char-casefold.c -o utf8-char-casefold -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt  -liconv -latomic
utf8-char-casefold.c:36:10: error: use of undeclared identifier 'FNM_CASEFOLD'
        flags = FNM_CASEFOLD;
                ^
1 error generated.