In this version, the binary actually is named clang-7 instead of
clang-7.0. This requires extending the test a little for keeping such
binaries but removing other clang-foo tools.
This doesn't help reduce the docker image size since it's done
in a separate RUN step than the one that added the files. (compiler-rt
and libunwind currently fail to build after stripping the llvm
installation though.)
Martin Storsjö