cc -pthread  -Wall -Wextra -Werror=implicit-function-declaration ctype/islower_l.c -o ctype/islower_l -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread  -liconv
ctype/islower_l.c:15:8: error: call to undeclared function 'islower_l'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   15 |         if ( !islower_l(c1, locale) )
      |               ^
ctype/islower_l.c:15:8: note: did you mean 'islower'?
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_ctype.h:254:1: note: 'islower' declared here
  254 | islower(int _c)
      | ^
1 error generated.