fix: defind ft macros & fix includes

Author: biraj21

src/client.c

@@ -1,4 +1,8 @@
+// feature test macro for getline() from man pages
+#define _POSIX_C_SOURCE 200809L
+
 #include <netdb.h>
+#include <signal.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>

src/server.c

@@ -1,3 +1,6 @@
+// feature test macro for getaddrinfo() from man pages
+#define _POSIX_C_SOURCE 200112L
+
 #include <netdb.h>      // for getaddrinfo()
 #include <poll.h>       // for poll()
 #include <signal.h>     // for signal()