Win: Attempt to keep from using Linux functions.

This is a hopefully-temporary solution to prevent some of the problems of
people breaking the Windows build while developing on Linux (or vice-versa).

This uses macros of the names of Linux/Windows-specific functions in order to
catch people who use those functions directly, instead of using the
platform-compatibility-layer functions.

In order to avoid problems with the layers #include'ing "loader_platform.h"
before they #include system files (which can mess them up), I #include
"loader_platform.h" twice.  The 2nd time, it #define's the hopefully-temporary
macros.

Note: For some reason, we can't #define LoadLibrary().  It generates warnings
on Windows.
diff --git a/layers/layers_config.cpp b/layers/layers_config.cpp
index b7d4e08..5528358 100644
--- a/layers/layers_config.cpp
+++ b/layers/layers_config.cpp
@@ -29,6 +29,9 @@
 #include <xglLayer.h>
 #include "loader_platform.h"
 #include "layers_config.h"
+// The following is #included again to catch certain OS-specific functions
+// being used:
+#include "loader_platform.h"
 
 #define MAX_CHARS_PER_LINE 4096