[openwrt/openwrt] imagebuilder: fix partition signature

[LEDE Commits]

aparcar pushed a commit to openwrt/openwrt.git, branch openwrt-19.07:
https://git.openwrt.org/5ecc7ead48783136569a541d59398e08767fd8bc

commit 5ecc7ead48783136569a541d59398e08767fd8bc
Author: Matthew Gyurgyik <matthew at gyurgyik.io>
AuthorDate: Fri Nov 13 11:21:29 2020 -0800

    imagebuilder: fix partition signature
    
    When building images with the imagebuilder, the partition signature
    never changes. The signature is generated by hashing SOURCE_DATE_EPOCH
    and LINUX_VERMAGIC which are undefined. Prepopulate these variables, as
    done by the SDK.
    
    Signed-off-by: Matthew Gyurgyik <matthew at gyurgyik.io>
    (cherry picked from commit aab36200e7eb539afb18df74476132f4750a9f0b)
---
 target/imagebuilder/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/target/imagebuilder/Makefile b/target/imagebuilder/Makefile
index 05c7cf3318..f1f25fc7c4 100644
--- a/target/imagebuilder/Makefile
+++ b/target/imagebuilder/Makefile
@@ -77,6 +77,8 @@ endif
 		$(CP) -L $(LINUX_DIR)/arch/$(LINUX_KARCH)/boot/dts/* $(IB_DTSDIR); \
 	fi
 	$(SED) 's,^# REVISION:=.*,REVISION:=$(REVISION),g' $(PKG_BUILD_DIR)/include/version.mk
+	$(SED) 's,^# SOURCE_DATE_EPOCH:=.*,SOURCE_DATE_EPOCH:=$(SOURCE_DATE_EPOCH),g' $(PKG_BUILD_DIR)/include/version.mk
+	$(SED) '/LINUX_VERMAGIC:=/ { s,unknown,$(LINUX_VERMAGIC),g }' $(PKG_BUILD_DIR)/include/kernel.mk
 	find $(PKG_BUILD_DIR) -name CVS -o -name .git -o -name .svn \
 	  | $(XARGS) rm -rf
 	$(INSTALL_DIR) $(IB_IDIR)