Only run debug tests if the build debug was built

configure

@@ -99,8 +99,10 @@ test: all
 	@for i in test/test*.js; do                         \\
 		echo "default \$\$i: ";                           \\
 		build/default/node \$\$i && \$(PASS) || \$(FAIL); \\
+    if [ -e build/debug/node ]; then                  \\
       echo "debug \$\$i: ";                           \\
       build/debug/node \$\$i && \$(PASS) || \$(FAIL); \\
+    fi;                                               \\
 	done 
 
 clean: