foo.c

/* confdefs.h.  */
#define PACKAGE_NAME "Haskell readline package"
#define PACKAGE_TARNAME "readline"
#define PACKAGE_VERSION "1.0"
#define PACKAGE_STRING "Haskell readline package 1.0"
#define PACKAGE_BUGREPORT "libraries@haskell.org"
/* end confdefs.h.  */

/* Override any GCC internal prototype to avoid an error.
   Use char because int might match the return type of a GCC
   builtin and then its argument prototype would still apply.  */
#ifdef __cplusplus
extern "C"
#endif
char readline ();
int
main ()
{
return readline ();
  ;
  return 0;
}

gistfile1.txt

$ gcc foo.c -o foo               
Undefined symbols:
  "_readline", referenced from:
      _main in ccWtaWV0.o
ld: symbol(s) not found
collect2: ld returned 1 exit status