Update license headers for compiler.

compiler/amxxpc/amxxpc.cpp

@@ -1,3 +1,12 @@
+// vim: set ts=4 sw=4 tw=99 noet:
+//
+// AMX Mod X, based on AMX Mod by Aleksander Naszko ("OLO").
+// Copyright (C) The AMX Mod X Development Team.
+//
+// This software is licensed under the GNU General Public License, version 3 or higher.
+// Additional exceptions apply. For full license details, see LICENSE.txt or visit:
+//     https://alliedmods.net/amxmodx-license
+
 #include <stdio.h>
 #if defined(__linux__) | defined (__APPLE__)
 #include <unistd.h>