ci: Add --disable-logs flag to per-commit-disabled-asserts job and use clang

Add the flag --disable-logs to the per-commit-disabled-asserts job. This job now tests ns-3 with both asserts and logs disabled.

Moreover, use the clang compiler, which has the flag clang-diagnostics-set-but-unused-variable to help detect variables that should be declared [[maybe_unused]] due to them only being used in asserts or log statements.