Use cmake TIMESTAMP function
Use cmake TIMESTAMP function

to allow to override build date with SOURCE_DATE_EPOCH
in order to make builds reproducible.
See https://reproducible-builds.org/ for why this is good
and https://reproducible-builds.org/specs/source-date-epoch/
for the definition of this variable.

Also use UTC to be independent of timezone.

alanxz/rabbitmq-c,alanxz/rabbitmq-c,alanxz/rabbitmq-c