TgaImporter: don't include these headers if not really needed.

src/Plugins/TgaImporter/TgaImporter.cpp

@@ -26,13 +26,16 @@
 
 #include <fstream>
 #include <sstream>
-#include <algorithm>
 #include <Utility/Endianness.h>
 #include <Math/Vector2.h>
 #include <ImageFormat.h>
-#include <Swizzle.h>
 #include <Trade/ImageData.h>
 
+#ifdef MAGNUM_TARGET_GLES
+#include <algorithm>
+#include <Swizzle.h>
+#endif
+
 #include "TgaHeader.h"
 
 namespace Magnum { namespace Trade { namespace TgaImporter {