Fix compile-time endianness check to work on linux. As the original comment says, it's still not very robust.

Sources/Plasma/NucleusLib/pnUtils/Private/pnUtEndian.h

@@ -46,13 +46,17 @@ You can contact Cyan Worlds, Inc. by email legal@cyan.com
 *
 ***/
 
-#ifdef _M_IX86
+#if defined(_M_IX86) || defined(i386) || defined(__i386__) || defined(__i386)
-# define LITTLE_ENDIAN  1
+# ifndef LITTLE_ENDIAN
+#  define LITTLE_ENDIAN  1
+# endif
 #else
-# define BIG_ENDIAN     1
+# ifndef BIG_ENDIAN
+#  define BIG_ENDIAN     1
 // That was a pretty weak check for endian-ness, if it
 // failed then we probably need to strengthen it a bit.
 # error "Are you sure this is a big-endian CPU?"
+# endif
 #endif