Code quality: Fix header guards consistency

Adds `header_guards.sh` bash script, used in CI to validate future
changes. Can be run locally to fix invalid header guards.

drivers/unix/dir_access_unix.cpp

@@ -516,4 +516,4 @@ DirAccessUnix::~DirAccessUnix() {
 	list_dir_end();
 }
 
-#endif //posix_enabled
+#endif // UNIX_ENABLED || LIBC_FILEIO_ENABLED

drivers/unix/dir_access_unix.h

@@ -90,5 +90,6 @@ public:
 	~DirAccessUnix();
 };
 
-#endif //UNIX ENABLED
-#endif
+#endif // UNIX_ENABLED || LIBC_FILEIO_ENABLED
+
+#endif // DIR_ACCESS_UNIX_H

drivers/unix/file_access_unix.cpp

@@ -339,4 +339,4 @@ FileAccessUnix::~FileAccessUnix() {
 	_close();
 }
 
-#endif
+#endif // UNIX_ENABLED || LIBC_FILEIO_ENABLED

drivers/unix/file_access_unix.h

@@ -86,5 +86,6 @@ public:
 	virtual ~FileAccessUnix();
 };
 
-#endif
-#endif
+#endif // UNIX_ENABLED || LIBC_FILEIO_ENABLED
+
+#endif // FILE_ACCESS_UNIX_H

drivers/unix/ip_unix.h

@@ -50,4 +50,5 @@ public:
 };
 
 #endif
+
 #endif // IP_UNIX_H

drivers/unix/net_socket_posix.h

@@ -28,8 +28,8 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#ifndef NET_SOCKET_UNIX_H
-#define NET_SOCKET_UNIX_H
+#ifndef NET_SOCKET_POSIX_H
+#define NET_SOCKET_POSIX_H
 
 #include "core/io/net_socket.h"
 
@@ -104,4 +104,4 @@ public:
 	~NetSocketPosix();
 };
 
-#endif
+#endif // NET_SOCKET_POSIX_H

drivers/unix/os_unix.h

@@ -98,6 +98,6 @@ public:
 	virtual ~UnixTerminalLogger();
 };
 
-#endif
+#endif // UNIX_ENABLED
 
-#endif
+#endif // OS_UNIX_H

drivers/unix/syslog_logger.h

@@ -43,6 +43,6 @@ public:
 	virtual ~SyslogLogger();
 };
 
-#endif
+#endif // UNIX_ENABLED
 
-#endif
+#endif // SYSLOG_LOGGER_H

drivers/unix/thread_posix.h

@@ -35,4 +35,4 @@
 void init_thread_posix();
 #endif
 
-#endif
+#endif // THREAD_POSIX_H