Update easylogging++ to 9.96.7, turn on /WX for clang-msvc

Updating from easylogging++ 9.89 to 9.96.7 turns it from a header only
library to one requiring a source file. It has been added to sources
near the other third party includes in the QMAKE to signify that it
isn't a first party file.

Updating easylogging++ also means that clang-msvc can compile without
any warnings, hence turning on warnings as errors for that compiler as
well, to avoid any regressions.

third-party/easylogging++/LICENSE

@@ -1,10 +1,11 @@
 The MIT License (MIT)
 
-Copyright (c) 2017 muflihun.com
+Copyright (c) 2012-2018 Zuhd Web Services
+Copyright (c) 2012-2018 @abumusamq
 
-http://github.com/easylogging/
-http://easylogging.muflihun.com
-http://muflihun.com
+https://github.com/zuhd-org/
+https://zuhd.org
+https://muflihun.com
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of
 this software and associated documentation files (the "Software"), to deal in