Adapt to the latest changes in Unikraft core

Adapt to the latest changes in Unikraft core

This commit updates various headers to match the latest posix-time
interface from Unikraft core, while also introducing new glue code
(`__uk_init_tls.c`) to adapt the library to the new TCB/TLS layout.

Checkpatch-Ignore: EMBEDDED_FUNCTION_NAME
Signed-off-by: Eduard Vintilă <eduard.vintila47@gmail.com>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Reviewed-by: Teodor Tiron <teotiron@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #28