[linux] Allow reproducible builds

[T4cC0re]

In a reproducible build all varied information is removed.
This patch does so, by checking if the standard SOURCE_DATE_EPOCH variable is set.
If it is, we are attempting a reproducible build and will strip varying information.

[eli-schwartz]

Thanks for working on this! Note that for reproducible builds we need to avoid embedding the time zone also, so that date call (for the SOURCE_DATE_EPOCH case) should also use -u.

See also "reading the variable": https://reproducible-builds.org/docs/source-date-epoch/

[T4cC0re]

@eli-schwartz Thanks for noticing. I just pushed an amended commit with the fix.

[masatake]

Could you update 00DIST file?

[masatake]

@ lrosenman, I will merge this though testing on freebsd is failed because the change is nothing to do with other dialect than Linux.

[lrosenman]

@masatake the FreeBSD CI is failed due to the Cirrus stuff using outdated images.
I'll see if I can figure out how to fix that for all 3 FreeBSD versions.

[masatake]

@lrosenman, thank you.

[T4cC0re]

@masatake Is there a procedure to updating the 00DIST file? Or do I just edit it by hand?

[masatake]

@T4cC0re, please, edit the file by hand directly.

[T4cC0re]

@masatake There is a Footnote in the bootom of the file with your name and a date. Should I change the date or leave it be?

[masatake]

Please, keep my name as is. Please, write what you did as an item like:

		[linux] fix a crash when printing the endpoint for unaccepted
		unix socket with +E option.
		This closes the github issue #74 reported by @jolmg.

The number of pull request (#94) and your name should be written in the item.

Updating 00CREDITS is ... my job.

[T4cC0re]

@masatake I updated the 00DIST file, does that look good to you?

[masatake]

@T4cC0re, yes thank you. I will merge this, and we will make a release in ... a month.

[lrosenman]

The FreeBSD CI images are changed in master now, but until #97 is merged they will fail. This should be fine to merge.

[masatake]

@lrosenman, though you merged #97, the tests of this pull request are failed.
Are they expected?

[lrosenman]

Yes, until I can get the kernel folks to look at the code and fix getting the executable and library names.

[masatake]

@lrosenman, I see. Thank you.
After updating 00CREDITS, I will merge this.

[masatake]

@T4cC0re, thank you.

[bmwiedemann]

In openSUSE, we had
https://github.com/bmwiedemann/openSUSE/blob/master/packages/l/lsof/lsof-no-build-date-etc.patch from 2010 for reproducible-builds that will soon not be needed anymore, thanks to this patch.