Symbiotic may fail to start when wrong clang binary is in PATH

[lzaoral]

For example, if we use a Debian based system with a suitable ccache symlink disguised as clang and without unversioned LLVM binaries in PATH, the initial sanity clang check in environment.py will succeed, however, the check for the rest of LLVM binaries in runtime.py will fail. Even though the correct ones are linked in install/llvm-${VERSION}/bin.

symbiotic --debug=all --dump-env-cmd
[DBG] Argv: /home/runner/work/symbiotic/symbiotic/tests/../scripts/symbiotic --debug=all --dump-env-cmd
[DBG] Symbiotic dir: /home/runner/work/symbiotic/symbiotic
[DBG] Did not find a build of LLVM, checking the system LLVM
|> clang -v
[DBG] 'clang' is '/usr/lib/ccache/clang'
ERROR: Could not find 'opt' executable

Probably the safest solution is to warn the user that ccache was detected, try to remove it from PATH and restart the whole procedure.