Set SOURCE_DATE_EPOCH to 1610550434.

This should help with determinism/reproducibility.

zlibs/bootstrap

@@ -29,6 +29,7 @@ bootstrap_complete_base()
 	export LANG=C
 	export LC_ALL=C
 	export DEBIAN_FRONTEND=noninteractive
+	export SOURCE_DATE_EPOCH=1610550434
 
 	bootstrap_cpio_stage3="$R/tmp/bootstrap-${os}-${arch}-stage3.cpio.gz"
 	bootstrap_cpio_stage4="$R/tmp/bootstrap-${os}-${arch}-stage4.cpio.gz"

zlibs/helpers

@@ -204,6 +204,7 @@ chroot-script()
 
 	sudo sed -i "$_path/$_script" \
 		-e 's@^#!/bin/sh@&\nexport DEBIAN_FRONTEND=noninteractive@' \
+		-e 's@^#!/bin/sh@&\nexport SOURCE_DATE_EPOCH=1610550434@' \
 		-e 's@^#!/bin/sh@&\nexport LC_ALL=C@' \
 		-e 's@^#!/bin/sh@&\nexport LANG=C@' \
 		-e 's@^#!/bin/sh@&\nset -x ; exec 2>/'$_script'.log@'