virtualbox does not build reproducibly

[bmwiedemann2]

meaning, it creates different results on every build. See  https://reproducible-builds.org/ why that matters.

This comes from multiple sources:

1. gzip needs to be called with -n (patch attached)

2. tar does not sort file lists by default (newer version have the --sort=name option but there are other solutions as well)

3. various .o files contain a 'VTG Object Header v1.7'

added in src/bldprogs/VBoxTpG.cpp:574 via src/VBox/Runtime/generic/RTUuidCreate-generic.cpp RTUuidCreate via src/VBox/Runtime/common/rand/rand.cpp RTRandBytes

IMHO, it would be better to replace that with some digest over source files, so that it changes whenever one of the inputs changes, but remains constant across builds.

[bmwiedemann2]

patch to not add timestamps to gz headers

[frank]

Makes sense, thanks for the hints.