package/pkg-generic: host variant inherits target download settings

It seems reasonable to expect that the download of the host and target
variants should usually be exactly the same and thus reuse the target
package values for the host package. This commits add support to
inherit host _DL_SUBDIR, _DOWNLOAD_DEPENDENCIES, _DL_ENV and
_DOwNLOAD_POST_PROCESS variables from target ones. These variables can
still be overriden if necessary for the host package.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit efa7712b092950c92f994e2ee30c120a64e5451b)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/pkg-generic.mk

@@ -540,6 +540,30 @@ ifndef $(2)_SUBDIR
  endif
 endif
 
+ifndef $(2)_DL_SUBDIR
+ ifdef $(3)_DL_SUBDIR
+  $(2)_DL_SUBDIR = $$($(3)_DL_SUBDIR)
+ endif
+endif
+
+ifndef $(2)_DOWNLOAD_DEPENDENCIES
+ ifdef $(3)_DOWNLOAD_DEPENDENCIES
+  $(2)_DOWNLOAD_DEPENDENCIES = $$(filter-out $(1),$$($(3)_DOWNLOAD_DEPENDENCIES))
+ endif
+endif
+
+ifndef $(2)_DL_ENV
+ ifdef $(3)_DL_ENV
+  $(2)_DL_ENV = $$($(3)_DL_ENV)
+ endif
+endif
+
+ifndef $(2)_DOWNLOAD_POST_PROCESS
+ ifdef $(3)_DOWNLOAD_POST_PROCESS
+  $(2)_DOWNLOAD_POST_PROCESS = $$($(3)_DOWNLOAD_POST_PROCESS)
+ endif
+endif
+
 ifndef $(2)_STRIP_COMPONENTS
  ifdef $(3)_STRIP_COMPONENTS
   $(2)_STRIP_COMPONENTS = $$($(3)_STRIP_COMPONENTS)