[source] build: ensure that flock is available for make download

[LEDE Commits]

jow pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/65eec8bd5f6337956b972d07fde49eb5db9cb4a0

commit 65eec8bd5f6337956b972d07fde49eb5db9cb4a0
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Jun 8 11:05:05 2017 +0200

    build: ensure that flock is available for make download
    
    It ensures that make download can parallelize downloads, even when some
    packages download the same files (e.g. gcc/initial, gcc/final)
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/toplevel.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/toplevel.mk b/include/toplevel.mk
index 77b04ae..1171c59 100644
--- a/include/toplevel.mk
+++ b/include/toplevel.mk
@@ -171,7 +171,7 @@ else
   DOWNLOAD_DIRS = package/download
 endif
 
-download: .config FORCE
+download: .config FORCE $(if $(wildcard $(TOPDIR)/staging_dir/host/bin/flock),,tools/flock/compile)
 	@+$(foreach dir,$(DOWNLOAD_DIRS),$(SUBMAKE) $(dir);)
 
 clean dirclean: .config