More SOURCE_DATE_EPOCH?

[wolfv]

I am looking into better support for "reproducible builds". I added support for SOURCE_DATE_EPOCH in one place in #140 - however, there are a few more timestamps in debug symbols or the strip command.

There is already a configuration option using ZERO_AR_DATE which works in all these places. It replaces the timestamp with a timestamp of 0.

I find SOURCE_DATE_EPOCH a little more elegant since it preserves a proper timestamp instead of setting it to some date in 1970. I would be happy to make the effort of enabling SOURCE_DATE_EPOCH in all places where ZERO_AR_DATE works right now. If we want to do it properly, we would probably change the interface / code in a few places though.

I haven't fully understood the relation to upstream in this repository. Would you accept a change like this? Do you know if I could contribute this back upstream to Apple as well?

A bigger change might be to replace fZeroModTimeInDebugMap with a timestamp and return a timestamp in zeroModTimeInDebugMap (or rename that function, even?).

Thanks!