Fix libmspack to compile with rbutil

The build system used by rbutil is not very robust: all the files
are eventually compiled to the same directory so we cannot have
two files with the same name (system.c would conflicts with
system.cpp) so rename one file to avoid this. Also change all
include directives to local ones because we don't have to expose
the entire mspack source to inclusion.

Change-Id: I3fe0638d69fdc30566eb9425abfe33c807678b28
Reviewed-on: http://gerrit.rockbox.org/417
Reviewed-by: Dominik Riebeling <Dominik.Riebeling@gmail.com>

rbutil/rbutilqt/mspack/kwajc.c

@@ -9,8 +9,8 @@
 
 /* KWAJ compression implementation */
 
-#include <system.h>
-#include <kwaj.h>
+#include "system-mspack.h"
+#include "kwaj.h"
 
 struct mskwaj_compressor *
   mspack_create_kwaj_compressor(struct mspack_system *sys)