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this flag was added added only recently which produces an error when used, for example, on Debian 12

Add new target `clean-external` to the Makefile, which triggers the
clean task of the respective buid system for each external simulator.
Each simulator can also be cleaned individually by using the targets
`{simulator name}-clean` (e.g. `gem5-clean`).

yapf takes a long time to run when this directory contains large output files

Otherwise make lint-clang-format still succeeds even if there are issues. This
also causes the github action to pass and not flag issues.

I basically did the following:
`mkdir experiments/simbricks/orchestration`
`mv experiments/simbricks/* experiments/simbricks/orchestration/`

Additionally, imports and paths had to be adjusted.

Only builds base image, none of the others.

for CFLAGS, CXXFLAGS, CPPFLAGS, VFLAGS

These are slower and currently yield a lot of warnings to be fixed.

Enables local persistent configuration of build variables.