Use %lld and %llu instead of %ld and %lu in time format

[sebastien.bini_stormshield.eu]

Summary

On our ARMv6 products, setting the date to 2038 will make date -e return a negative time.

> date 2038-07-07
> date -e
-2132932729
>

It all comes down to libc's strftime. It uses long which are 32bit long on arm.
This causes an overflow and explains the negative value.

[imp]

You could also do the intmx_t dance, but this is honestly fine.