cmake HAVE_STRLOG examples

syslog-ng/syslog-ng modules/afstreams/CMakeLists.txt :12

check_c_source_compiles("
  #include <sys/strlog.h>
  struct strbuf b;
  int main(void) {
    struct log_ctl lc;
    lc.mid = 0;
    return 0;
  }
" HAVE_STRLOG)