verify if there is library function defined (like autoconf's AC_CHECK_LIB)

has_broken_mac_readline.sh

has_broken_mac_readline() {
  # MacOSX 10.4 has a broken readline.
  # https://github.com/yyuu/pyenv/issues/23
  local retval=1
  local conftest="$BUILD_PATH/has_broken_mac_readline.c"
  if [ "$(uname -s)" = "Darwin" ]; then
    cat <<EOF > "$conftest"
#ifdef __cplusplus
extern "C"
#endif
char rl_gnu_readline_p ();
int main() { return rl_gnu_readline_p (); return 0; }
EOF
    { "$CC" -o "/dev/null" $CFLAGS $CPPFLAGS $LDFLAGS "$conftest" -lreadline
    } || retval=0
    rm -f "$conftest"
  fi
  return "$retval"
}