The DST characteristics of the POSIX EST5EDT and CST6CDT timezones
depend on whether the implementation uses the built-in POSIX definition
or reads an updated version from the tzdata files, and for POSIX
timezones, there is no specified behavior [1].
To avoid any plaform-specific behavior, we can specify the desired DST
ourselves. We used the timezone values available in
configure/CONFIG_SITE_ENV, which already included DST information, and
means the tests are consistent with our own usage.
[1] https://www.openwall.com/lists/musl/2024/03/05/2
In some cases the license-identification header was missing,
so I added that as well. Replaced the remaining headers that
specifically identified "Versions 3.13.7 and higher".
Makefiles and the build system were deliberately excluded.
Érico Nogueira