[source] build: skip opkg host dependency within the SDK

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/0aa46bf76ab01fe1f64b0992fe2a8196c3b19d89

commit 0aa46bf76ab01fe1f64b0992fe2a8196c3b19d89
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Tue Feb 21 20:43:35 2017 +0100

    build: skip opkg host dependency within the SDK
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 package/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/package/Makefile b/package/Makefile
index 1ef5017..ac8faec 100644
--- a/package/Makefile
+++ b/package/Makefile
@@ -56,7 +56,9 @@ $(curdir)/merge:
 $(curdir)/merge-index: $(curdir)/merge
 	(cd $(PACKAGE_DIR_ALL) && $(SCRIPT_DIR)/ipkg-make-index.sh . 2>&1 > Packages; )
 
-$(curdir)/compile: $(curdir)/system/opkg/host/compile
+ifndef SDK
+  $(curdir)/compile: $(curdir)/system/opkg/host/compile
+endif
 
 $(curdir)/install: $(TMP_DIR)/.build $(curdir)/merge $(if $(CONFIG_TARGET_PER_DEVICE_ROOTFS),$(curdir)/merge-index)
 	- find $(STAGING_DIR_ROOT) -type d | $(XARGS) chmod 0755