Generating deterministic timestamp in order to make the builds reproducible
Whilst working on the Reproducible Builds effort, we noticed that verilator could not be built reproducibly as it uses current time and date in the generated 'vlt_dump.vcd' file.
This patch ensures that the output is consistent regardless of the build user's current time by utilizing the
SOURCE_DATE_EPOCH environment variable.
Let me know if you have any questions or queries regarding this patch.