Userspace: Add missing #includes now that AK/StdLibExtras.h is smaller

Libraries/LibCore/ArgsParser.cpp

@@ -29,6 +29,7 @@
 #include <getopt.h>
 #include <limits.h>
 #include <stdio.h>
+#include <string.h>
 
 namespace Core {
 

Libraries/LibCore/DirIterator.h

@@ -28,6 +28,7 @@
 
 #include <AK/String.h>
 #include <dirent.h>
+#include <string.h>
 
 namespace Core {
 

Libraries/LibCore/IODevice.cpp

@@ -30,6 +30,7 @@
 #include <LibCore/SyscallUtils.h>
 #include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/select.h>
 #include <sys/stat.h>
 #include <sys/time.h>

Libraries/LibCore/SocketAddress.h

@@ -29,6 +29,7 @@
 #include <AK/IPv4Address.h>
 #include <arpa/inet.h>
 #include <netinet/in.h>
+#include <string.h>
 #include <sys/socket.h>
 #include <sys/un.h>
 

Libraries/LibCore/SyscallUtils.h

@@ -29,6 +29,7 @@
 #include <AK/LogStream.h>
 #include <AK/StdLibExtras.h>
 #include <errno.h>
+#include <string.h>
 #include <sys/types.h>
 #include <unistd.h>