From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sun, 24 Apr 2016 08:48:45 +0200
Subject: build: add locking for downloads (fixes race conditions with multiple variants)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Backport of r48416

diff --git a/include/download.mk b/include/download.mk
index e518cce..9176b11 100644
--- a/include/download.mk
+++ b/include/download.mk
@@ -182,6 +182,6 @@ define Download
 
   $(DL_DIR)/$(FILE):
 	mkdir -p $(DL_DIR)
-	$(if $(DownloadMethod/$(call dl_method,$(URL),$(PROTO))),$(DownloadMethod/$(call dl_method,$(URL),$(PROTO))),$(DownloadMethod/unknown))
+	$(call locked,$(if $(DownloadMethod/$(call dl_method,$(URL),$(PROTO))),$(DownloadMethod/$(call dl_method,$(URL),$(PROTO))),$(DownloadMethod/unknown)),$(FILE))
 
 endef