[source] sdk: predefine SOURCE_DATE_EPOCH

[LEDE Commits]

jow pushed a commit to source.git, branch master:
https://git.lede-project.org/8cc922411561dfa6f65fbb492a7bdb6fb9bbb6d5

commit 8cc922411561dfa6f65fbb492a7bdb6fb9bbb6d5
Author: Jo-Philipp Wich <jo at mein.io>
AuthorDate: Fri Oct 21 12:21:40 2016 +0200

    sdk: predefine SOURCE_DATE_EPOCH
    
    When building packages within the SDK, there is no Git revision history
    available so prepopulate SOURCE_DATE_EPOCH in version.mk, similar to
    how we handle REVISION already.
    
    Acked-by: Felix Fietkau <nbd at nbd.name>
    Signed-off-by: Jo-Philipp Wich <jo at mein.io>
---
 include/toplevel.mk | 3 ++-
 include/version.mk  | 1 +
 target/sdk/Makefile | 1 +
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/toplevel.mk b/include/toplevel.mk
index e13acaf..81329ac 100644
--- a/include/toplevel.mk
+++ b/include/toplevel.mk
@@ -16,13 +16,14 @@ ifeq ($(SDK),1)
   include $(TOPDIR)/include/version.mk
 else
   REVISION:=$(shell $(TOPDIR)/scripts/getver.sh)
+  SOURCE_DATE_EPOCH:=$(shell $(TOPDIR)/scripts/get_source_date_epoch.sh)
 endif
 
 HOSTCC ?= $(CC)
 export REVISION
+export SOURCE_DATE_EPOCH
 export GIT_CONFIG_PARAMETERS='core.autocrlf=false'
 export MAKE_JOBSERVER=$(filter --jobserver%,$(MAKEFLAGS))
-export SOURCE_DATE_EPOCH:=$(shell $(TOPDIR)/scripts/get_source_date_epoch.sh)
 
 # prevent perforce from messing with the patch utility
 unexport P4PORT P4USER P4CONFIG P4CLIENT
diff --git a/include/version.mk b/include/version.mk
index b54eaab..4beaca6 100644
--- a/include/version.mk
+++ b/include/version.mk
@@ -8,6 +8,7 @@
 
 # Substituted by SDK, do not remove
 # REVISION:=x
+# SOURCE_DATE_EPOCH:=x
 
 RELEASE:=Reboot
 
diff --git a/target/sdk/Makefile b/target/sdk/Makefile
index 77695ee..0688904 100644
--- a/target/sdk/Makefile
+++ b/target/sdk/Makefile
@@ -118,6 +118,7 @@ $(BIN_DIR)/$(SDK_NAME).tar.bz2: clean
 		cat $(TOPDIR)/feeds.conf.default >> $(SDK_BUILD_DIR)/feeds.conf.default; \
 	fi
 	$(SED) 's,^# REVISION:=.*,REVISION:=$(REVISION),g' $(SDK_BUILD_DIR)/include/version.mk
+	$(SED) 's,^# SOURCE_DATE_EPOCH:=.*,SOURCE_DATE_EPOCH:=$(SOURCE_DATE_EPOCH),g' $(SDK_BUILD_DIR)/include/version.mk
 	$(SED) '/LINUX_VERMAGIC:=/ { s,unknown,$(LINUX_VERMAGIC),g }' $(SDK_BUILD_DIR)/include/kernel.mk
 	find $(SDK_BUILD_DIR) -name .git | $(XARGS) rm -rf
 	find $(SDK_BUILD_DIR) -name .svn | $(XARGS) rm -rf