check that the makefile exists and stop if it doesnt

build-support/factor.sh

@@ -339,7 +339,19 @@ cd_factor() {
     check_ret cd
 }
 
+check_makefile_exists() {
+    if [[ ! -e "Makefile" ]] ; then
+        echo ""
+        echo "***Makefile not found***"
+        echo "You are likely in the wrong directory."
+        echo "Run this script from your factor directory:"
+        echo "     ./build-support/factor.sh"
+        exit 6
+    fi
+}
+
 invoke_make() {
+    check_makefile_exists
     $MAKE $MAKE_OPTS $*
     check_ret $MAKE
 }