[tex-live] Fixed compilation date in the .log file

[Akira Kakuto]

> I guess this is done on purpose by the l3build system to avoid
> differences when checking regression files.  I had never noticed this
> before :-(

Many thanks. I didn't know that. I can find in
l3build-aux.lua:

function setepoch()
  return
    os_setenv .. " SOURCE_DATE_EPOCH=" .. epoch
      .. os_concat ..
    os_setenv .. " SOURCE_DATE_EPOCH_TEX_PRIMITIVES=1"
      .. os_concat ..
    os_setenv .. " FORCE_SOURCE_DATE=1"
      .. os_concat
end

Best,
Akira