* Makefile.am (today): Consistently print the UTC date in C locale. * configure.ac (RPM_CHANGELOGTIME, DEB_CHANGELOGTIME): Likewise. * maint/update_copyright_years.sh: Likewise. * copyright-year-gen: Likewise. When $SOURCE_DATE_EPOCH is non-empty, use it as fallback date before the current system date. References: https://github.com/strace/strace/pull/68