opkg: Fix build reproducibility issue

A build date was leaking into the generated docs and makefile used for
ptests leading to reproducibility issues each time the month changed.

Add a patch to use SOURCE_DATE_EPOCH to derive it if available.

(From OE-Core rev: 61c639fcfdaa0a14e2a6a2bcca3215f99af94634)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 6a9ca7aec4991eabd425e32fdf85f51bb1686b8b)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/opkg/opkg/sourcedateepoch.patch

@@ -0,0 +1,25 @@
+Having CLEAN_DATE come from the current date doesn't allow for build
+reproducibility. Add the option of using SOURCE_DATE_EPOCH if set
+which for OE, it will be.
+
+Upstream-Status: Pending
+RP 2021/2/2
+
+Index: opkg-0.4.4/configure.ac
+===================================================================
+--- opkg-0.4.4.orig/configure.ac
++++ opkg-0.4.4/configure.ac
+@@ -281,7 +281,12 @@ AC_FUNC_UTIME_NULL
+ AC_FUNC_VPRINTF
+ AC_CHECK_FUNCS([memmove memset mkdir regcomp strchr strcspn strdup strerror strndup strrchr strstr strtol strtoul sysinfo utime])
+ 
+-CLEAN_DATE=`date +"%B %Y" | tr -d '\n'`
++1607446883
++if [ ! -z "$SOURCE_DATE_EPOCH" ]; then
++    CLEAN_DATE=`LC_ALL=C date -d @$SOURCE_DATE_EPOCH +"%B %Y" | tr -d '\n'`
++else
++    CLEAN_DATE=`date +"%B %Y" | tr -d '\n'`
++fi
+ 
+ AC_SUBST([CLEAN_DATE])
+ 

meta/recipes-devtools/opkg/opkg_0.4.2.bb

@@ -14,6 +14,7 @@ PE = "1"
 SRC_URI = "http://downloads.yoctoproject.org/releases/${BPN}/${BPN}-${PV}.tar.gz \
            file://opkg.conf \
            file://0001-opkg_conf-create-opkg.lock-in-run-instead-of-var-run.patch \
+           file://sourcedateepoch.patch \
            file://run-ptest \
 "