Version information not updated in local build

[krichardsson]

The version information is handled by generating a c file, build/src/utils/src/version_gen.c that is compiled into the firmware.
This works fine when building from a newly cloned repo but when building locally in an "old" file tree, version_gen.c is not updated and the version that is compiled into the firmware is stale.
make clean does not remove the file either.

I found traces in tools/kbuild/Makefile.kbuild (search for 'version_h') that looks like an old implementation of forcing the build of version information, but it is targeted at version.h and does not work.