scons: 3.0.3 -> 3.0.4

Announcement:
https://scons.org/scons-304-is-available.html

Changelog:
https://raw.githubusercontent.com/SConsProject/scons/rel_3.0.4/src/CHANGES.txt

There where no regressions and no deprecations in this release (at least
it does not break any additional builds in nixpkgs).