util, io, net, ...: use "#pragma once"

src/net/IPv4Address.hxx

@@ -1,8 +1,7 @@
 // SPDX-License-Identifier: BSD-2-Clause
 // author: Max Kellermann <max.kellermann@gmail.com>
 
-#ifndef IPV4_ADDRESS_HXX
-#define IPV4_ADDRESS_HXX
+#pragma once
 
 #include "SocketAddress.hxx"
 #include "util/ByteOrder.hxx"
@@ -209,5 +208,3 @@ public:
 				   GetPort() & other.GetPort());
 	}
 };
-
-#endif

src/net/IPv6Address.hxx

@@ -1,8 +1,7 @@
 // SPDX-License-Identifier: BSD-2-Clause
 // author: Max Kellermann <max.kellermann@gmail.com>
 
-#ifndef IPV6_ADDRESS_HXX
-#define IPV6_ADDRESS_HXX
+#pragma once
 
 #include "SocketAddress.hxx"
 #include "util/ByteOrder.hxx"
@@ -191,5 +190,3 @@ private:
 			   : (0xffff << (offset + 16 - prefix_length)));
 	}
 };
-
-#endif

src/net/Resolver.hxx

@@ -2,8 +2,7 @@
 // Copyright CM4all GmbH
 // author: Max Kellermann <mk@cm4all.com>
 
-#ifndef NET_RESOLVER_HXX
-#define NET_RESOLVER_HXX
+#pragma once
 
 class AddressInfoList;
 
@@ -30,5 +29,3 @@ Resolve(const char *host_and_port, int default_port,
 
 AddressInfoList
 Resolve(const char *host_port, unsigned default_port, int flags, int socktype);
-
-#endif