pkg-infra: move the scp download helper to a script

Maintaining the download helpers in the Makefile has proved to be a bit
complex, so move it to a shell script.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/pkg-download.mk

@@ -14,7 +14,7 @@ export CVS := $(call qstrip,$(BR2_CVS))
 export BZR := $(call qstrip,$(BR2_BZR))
 export GIT := $(call qstrip,$(BR2_GIT))
 export HG := $(call qstrip,$(BR2_HG)) $(QUIET)
-SCP := $(call qstrip,$(BR2_SCP)) $(QUIET)
+export SCP := $(call qstrip,$(BR2_SCP)) $(QUIET)
 SSH := $(call qstrip,$(BR2_SSH)) $(QUIET)
 LOCALFILES := $(call qstrip,$(BR2_LOCALFILES))
 
@@ -147,7 +147,8 @@ endef
 # to prepend the path with a slash: scp://[user@]host:/absolutepath
 define DOWNLOAD_SCP
 	test -e $(DL_DIR)/$(2) || \
-	$(SCP) '$(call stripurischeme,$(call qstrip,$(1)))' $(DL_DIR)/$(2)
+	$(EXTRA_ENV) support/download/scp '$(call stripurischeme,$(call qstrip,$(1)))' \
+					  $(DL_DIR)/$(2)
 endef
 
 define SOURCE_CHECK_SCP

support/download/scp

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+# We want to catch any command failure, and exit immediately
+set -e
+
+# Download helper for scp
+# Call it with:
+#   $1: URL
+#   $2: output file
+# And this environment:
+#   SCP       : the scp command to call
+
+url="${1}"
+output="${2}"
+
+${SCP} "${url}" "${output}"