Cleanup header files

- All now include maxscale/cdefs.h as the very first file.
- MXS_[BEGIN|END]_DECLS added to all C-headers.
  Strictly speaking not necessary for private headers, but
  does not hurt either.
- Include guards moved to the very top of the file.
- #pragma once added.

include/maxscale/mysql_utils.h

@@ -1,5 +1,6 @@
-#ifndef _MYSQL_UTILS_H
-#define _MYSQL_UTILS_H
+#pragma once
+#ifndef _MAXSCALE_MYSQL_UTILS_H
+#define _MAXSCALE_MYSQL_UTILS_H
 /*
  * Copyright (c) 2016 MariaDB Corporation Ab
  *
@@ -13,11 +14,14 @@
  * Public License.
  */
 
+#include <maxscale/cdefs.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <mysql.h>
 #include <maxscale/server.h>
 
+MXS_BEGIN_DECLS
+
 /** Length-encoded integers */
 size_t leint_bytes(uint8_t* ptr);
 uint64_t leint_value(uint8_t* c);
@@ -27,7 +31,8 @@ uint64_t leint_consume(uint8_t ** c);
 char* lestr_consume_dup(uint8_t** c);
 char* lestr_consume(uint8_t** c, size_t *size);
 
-
 MYSQL *mxs_mysql_real_connect(MYSQL *mysql, SERVER *server, const char *user, const char *passwd);
 
+MXS_END_DECLS
+
 #endif