Fix for T2

see: http://dev.vba-m.com/T2

> Every time I launch a server it defaults to the locahost IP instead of my
> actual IP. This is preventing me from linking with friends over Hamachi. When
> they enter my IP it errors on their end and they cannot connect. [report taken
> from <https://sourceforge.net/p/vbam/bugs/219/>]

Also, by chance, added the build folder to `.gitignore` so as to not pollute the
git repo.  I meant to do them as separate commits, but I forgot to do so.

Signed-off-by: Jonathan Sifuentes <jayands2k11@ymail.com>

.gitignore

@@ -4,3 +4,5 @@ src/wx/cmd-evtable.h
 src/wx/cmdhandlers.h
 src/wx/cmdtab.cpp
 src/wx/wxvbam.xrs
+build/
+

src/gba/GBASockClient.cpp

@@ -7,7 +7,7 @@
 GBASockClient::GBASockClient(sf::IpAddress _server_addr)
 {
     if (_server_addr == sf::IpAddress::None)
-        server_addr = sf::IpAddress::LocalHost;
+        server_addr = sf::IpAddress::getPublicAddress();
     else
         server_addr = _server_addr;
 

src/gba/GBASockClient.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cstdlib>
+#include <cstdint>
 #include <SFML/Network.hpp>
 
 class GBASockClient {