/opt/IBM/openxlC/17.1.1/bin/ibm-clang -pthread   -Wall -Wextra -Werror=implicit-function-declaration casefold-bracket-equivclass.c -o casefold-bracket-equivclass -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt  -liconv -latomic
casefold-bracket-equivclass.c:21:10: error: use of undeclared identifier 'FNM_CASEFOLD'
        flags = FNM_CASEFOLD;
                ^
1 error generated.