Switched to header only spdlog for better portability

thirdparty/spdlog/fwd.h

@@ -0,0 +1,14 @@
+// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
+// Distributed under the MIT License (http://opensource.org/licenses/MIT)
+
+#pragma once
+
+namespace spdlog {
+class logger;
+class formatter;
+
+namespace sinks {
+class sink;
+}
+
+} // namespace spdlog