According to CodeSearch, there's quite a few packages that will embed the date and time of the build.

Usage of these macros must simply be removed.

gcc-4.9 introduced a new warning -Wdate-time which will warn when they are used. dpkg-buildflags from dpkg 1.17.14 or later passes -Wdate-time to debian/rules when DEB_BUILD_MAINT_OPTIONS=reproducible=+timeless is set. We need to follow some steps before this can be turned on by default. Eventually the warnings can be turned into errors with the -Werror=date-time flag. The reproducible builds branch of dpkg does both of these things.