scripts/build: ensure that $PKG_BUILD is always created

... even if no unpack is called...

closes #2811

scripts/build

@@ -50,6 +50,11 @@ STAMP=$STAMPS/$PACKAGE_NAME/build_$TARGET
 
 $SCRIPTS/unpack $PACKAGE_NAME
 
+# ensure $PKG_BUILD is there. (installer? PKG_URL="")
+if [ ! -d $PKG_BUILD ] ; then
+  mkdir  $PKG_BUILD
+fi
+
 if [ -f $PKG_DIR/package.mk ]; then
   if [ -f $STAMP -a $PKG_DIR/package.mk -nt $STAMP ]; then
     rm -f $STAMP