support argument use=gen2 to support the new NIOS2 gen2 processor

tools/quartus/run_app

@@ -98,6 +98,9 @@ for arg ; do
         use=qsys)
             userflags="-DCOMPILE_FOR_QSYS"
             ;;
+        use=gen2)
+            userflags="-DCOMPILE_FOR_GEN2"
+            ;;
         *=* )
             # it was an option. skip it - if we wanted to,
             # we could process them over here