Reproducible builds requires that the build time stamp is not

Reproducible builds requires that the build time stamp is not

recorded in binaries. In FPC they are fuild in via the $INCLUDE %DATE%
directive which calls getdatestr in globals.pas. To allow reproducible builds
we should honor the SOURCE_DATE_EPOCH environment variable. To not depend on
the dateutil unit, we include the required code from that package here.

Gbp-Pq: Name honor_SOURCE_DATE_EPOCH_in_date.patch