refactor: replace manual header guards with #pragma once

It is less error-prone than manually defining header guards. Pretty much
all compilers support it even if it's not part of the C standard.

src/nvim/msgpack_rpc/channel.h

@@ -1,5 +1,4 @@
-#ifndef NVIM_MSGPACK_RPC_CHANNEL_H
-#define NVIM_MSGPACK_RPC_CHANNEL_H
+#pragma once
 
 #include <stdbool.h>
 #include <uv.h>
@@ -22,4 +21,3 @@ EXTERN MultiQueue *ch_before_blocking_events INIT( = NULL);
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "msgpack_rpc/channel.h.generated.h"
 #endif
-#endif  // NVIM_MSGPACK_RPC_CHANNEL_H

src/nvim/msgpack_rpc/channel_defs.h

@@ -1,5 +1,4 @@
-#ifndef NVIM_MSGPACK_RPC_CHANNEL_DEFS_H
-#define NVIM_MSGPACK_RPC_CHANNEL_DEFS_H
+#pragma once
 
 #include <msgpack.h>
 #include <stdbool.h>
@@ -49,5 +48,3 @@ typedef struct {
   Dictionary info;
   ClientType client_type;
 } RpcState;
-
-#endif  // NVIM_MSGPACK_RPC_CHANNEL_DEFS_H

src/nvim/msgpack_rpc/helpers.h

@@ -1,5 +1,4 @@
-#ifndef NVIM_MSGPACK_RPC_HELPERS_H
-#define NVIM_MSGPACK_RPC_HELPERS_H
+#pragma once
 
 #include <msgpack.h>
 #include <stdbool.h>
@@ -19,5 +18,3 @@
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "msgpack_rpc/helpers.h.generated.h"
 #endif
-
-#endif  // NVIM_MSGPACK_RPC_HELPERS_H

src/nvim/msgpack_rpc/server.h

@@ -1,9 +1,7 @@
-#ifndef NVIM_MSGPACK_RPC_SERVER_H
-#define NVIM_MSGPACK_RPC_SERVER_H
+#pragma once
 
 #include <stdio.h>
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "msgpack_rpc/server.h.generated.h"
 #endif
-#endif  // NVIM_MSGPACK_RPC_SERVER_H

src/nvim/msgpack_rpc/unpacker.h

@@ -1,5 +1,4 @@
-#ifndef NVIM_MSGPACK_RPC_UNPACKER_H
-#define NVIM_MSGPACK_RPC_UNPACKER_H
+#pragma once
 
 #include <inttypes.h>
 #include <stdbool.h>
@@ -49,5 +48,3 @@ struct Unpacker {
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "msgpack_rpc/unpacker.h.generated.h"
 #endif
-
-#endif  // NVIM_MSGPACK_RPC_UNPACKER_H