address compiler warnings (#861)

* Fixes unknown-pragma warnings for non-MSC compilers
  in `LocklessQueue.h`.
* Suppress 64-to-32-bit shortening compiler warning for
  newer versions of MSC (warning 4244) in `websocketpp_websocket.cpp`.

Author: eofenstein

Diff for: Source/Task/LocklessQueue.h

@@ -56,8 +56,10 @@
  ******************************************************************************/
 
 // LocklessQueue needs certain alignment.  Disable alignment warning.
+#if _WIN32
 #pragma warning(push)
 #pragma warning(disable: 4324)
+#endif
 
 template <typename TData>
 class alignas(8) LocklessQueue
@@ -868,4 +870,6 @@ class alignas(8) LocklessQueue
     }
 };
 
+#if _WIN32
 #pragma warning(pop)
+#endif

Diff for: Source/WebSocket/Websocketpp/websocketpp_websocket.cpp

@@ -18,7 +18,7 @@
 
 #ifdef _WIN32
 #pragma warning( push )
-#pragma warning( disable : 4100 4127 4512 4996 4701 4267 )
+#pragma warning( disable : 4100 4127 4512 4996 4701 4267 4244 )
 #define _WEBSOCKETPP_CPP11_STL_
 #define _WEBSOCKETPP_CONSTEXPR_TOKEN_
 #define _SCL_SECURE_NO_WARNINGS
@@ -31,8 +31,6 @@
 #pragma clang diagnostic ignored "-Wshorten-64-to-32"
 #endif
 
-#pragma warning(disable: 4244) 
-
 #include <websocketpp/config/asio_client.hpp>
 #include <websocketpp/config/asio_no_tls_client.hpp>
 #include <websocketpp/client.hpp>