Fix GPP Makefile usage to Makefile.xt. Reported by Armijn Hemel
Fix GPP Makefile usage to Makefile.xt. Reported by Armijn Hemel

svn path=/trunk/StrategoXT/; revision=2104

lichtemo/strategoxt,metaborg/strategoxt,Apanatshka/strategoxt,Apanatshka/strategoxt,Apanatshka/strategoxt,lichtemo/strategoxt,Apanatshka/strategoxt,lichtemo/strategoxt,metaborg/strategoxt,Apanatshka/strategoxt,lichtemo/strategoxt,metaborg/strategoxt,metaborg/strategoxt,lichtemo/strategoxt,metaborg/strategoxt