[tex-live] Extending SOURCE_DATE_EPOCH support

[Akira Kakuto]

> The patches for the other engines look definitely worth considering,
> and I consider sending it with explanations to the tex-k at tug.org
> mailing list, which is a better place, as the development of TeX Live
> will not change things in the engines.

(1) SOURCE_DATE_EPOCH support in (x)dvipdfmx is by myself,
    so I'll apply the patch for (x)dvipdfmx.

(2) The texmfmp.c is mainly maintained by Karl, so Karl will
    determine to apply the patch or not.

(3) luatex is developed by the LuaTeX team, mainly
    Hans, and Luigi recently.

Best,
Akira